Backup doesn't finish and get's slow

Hi, i have 3 Backups running. Two of them have no problems. The third one allways hangs after a while and does not end. Then i have to stop the prozess Duplicati.WindowsService and start the Service again.

I see that the BackendSpeed is getting very slow while the backup is running. It starts with 40 KB and after 50000 files BackendSpeed is 133 bytes/s. The backupup has over 100000 files (emails).

What can i do?

Here some more infos:
Server Zustandseigenschaften

lastEventId : 72
lastDataUpdateId : 15
lastNotificationUpdateId : 4
estimatedPauseEnd : 0001-01-01T00:00:00
activeTask : {"Item1":4,"Item2":"8"}
programState : Running
lastErrorMessage :
connectionState : connected
xsfrerror : false
connectionAttemptTimer : 0
failedConnectionAttempts : 0
lastPgEvent : {"BackupID":"8","TaskID":4,"BackendAction":"Put","BackendPath":"ParallelUpload","BackendFileSize":5247327514,"BackendFileProgress":3808784179,"BackendSpeed":557286,"BackendIsBlocking":false,"CurrentFilename":"F:\\Backup\\hmail\\Data\\DATA\\archiv\\02\\{DATA-71F8E9B9CCE2}.eml","CurrentFilesize":5577280,"CurrentFileoffset":5577280,"CurrentFilecomplete":true,"Phase":"Backup_ProcessingFiles","OverallProgress":0,"ProcessedFileCount":107186,"ProcessedFileSize":55820484306,"TotalFileCount":108276,"TotalFileSize":56267580094,"StillCounting":false}
updaterState : Waiting
updatedVersion :
updateReady : false
updateDownloadProgress : 0
proposedSchedule : [{"Item1":"2","Item2":"2020-05-26T17:00:00Z"},{"Item1":"3","Item2":"2020-05-26T17:00:00Z"},{"Item1":"8","Item2":"2020-05-26T21:00:00Z"}]
schedulerQueueIds : []
pauseTimeRemain : 0

System-Eigenschaften

APIVersion : 1
PasswordPlaceholder : **********
ServerVersion : 2.0.5.106
ServerVersionName : - 2.0.5.106_canary_2020-05-11
ServerVersionType : Canary
StartedBy : Server
BaseVersionName : 2.0.5.1_beta_2020-01-18
DefaultUpdateChannel : Canary
DefaultUsageReportLevel : Information
ServerTime : 2020-05-26T12:12:49.9930325+02:00
OSType : Windows
DirectorySeparator : \
PathSeparator : ;
CaseSensitiveFilesystem : false
MonoVersion :
MachineName : S02
UserName : SYSTEM
NewLine :
CLRVersion : 4.0.30319.42000
CLROSInfo : {"Platform":"Win32NT","ServicePack":"","Version":"10.0.14393.0","VersionString":"Microsoft Windows NT 10.0.14393.0"}
ServerModules : []
UsingAlternateUpdateURLs : false
LogLevels : ["ExplicitOnly","Profiling","Verbose","Retry","Information","DryRun","Warning","Error"]
SuppressDonationMessages : false
SpecialFolders : [{"ID":"%APPDATA%","Path":"C:\\Windows\\system32\\config\\systemprofile\\AppData\\Roaming"},{"ID":"%HOME%","Path":"C:\\Windows\\system32\\config\\systemprofile"}]
BrowserLocale : {"Code":"de","EnglishName":"German","DisplayName":"Deutsch"}
SupportedLocales : [{"Code":"bn","EnglishName":"Bangla","DisplayName":"বাংলা"},{"Code":"ca","EnglishName":"Catalan","DisplayName":"català"},{"Code":"cs","EnglishName":"Czech","DisplayName":"čeština"},{"Code":"da","EnglishName":"Danish","DisplayName":"dansk"},{"Code":"de","EnglishName":"German","DisplayName":"Deutsch"},{"Code":"en","EnglishName":"English","DisplayName":"English"},{"Code":"en-GB","EnglishName":"English (United Kingdom)","DisplayName":"English (United Kingdom)"},{"Code":"es","EnglishName":"Spanish","DisplayName":"español"},{"Code":"fi","EnglishName":"Finnish","DisplayName":"suomi"},{"Code":"fr","EnglishName":"French","DisplayName":"français"},{"Code":"fr-CA","EnglishName":"French (Canada)","DisplayName":"français (Canada)"},{"Code":"hu","EnglishName":"Hungarian","DisplayName":"magyar"},{"Code":"it","EnglishName":"Italian","DisplayName":"italiano"},{"Code":"ja-JP","EnglishName":"Japanese (Japan)","DisplayName":"日本語 (日本)"},{"Code":"ko","EnglishName":"Korean","DisplayName":"한국어"},{"Code":"lt","EnglishName":"Lithuanian","DisplayName":"lietuvių"},{"Code":"lv","EnglishName":"Latvian","DisplayName":"latviešu"},{"Code":"nl-NL","EnglishName":"Dutch (Netherlands)","DisplayName":"Nederlands (Nederland)"},{"Code":"pl","EnglishName":"Polish","DisplayName":"polski"},{"Code":"pt","EnglishName":"Portuguese","DisplayName":"português"},{"Code":"pt-BR","EnglishName":"Portuguese (Brazil)","DisplayName":"português (Brasil)"},{"Code":"ro","EnglishName":"Romanian","DisplayName":"română"},{"Code":"ru","EnglishName":"Russian","DisplayName":"русский"},{"Code":"sk","EnglishName":"Slovak","DisplayName":"slovenčina"},{"Code":"sk-SK","EnglishName":"Slovak (Slovakia)","DisplayName":"slovenčina (Slovensko)"},{"Code":"sr-RS","EnglishName":"Unknown Locale (sr-RS)","DisplayName":"Unbekanntes Gebietsschema (sr-RS)"},{"Code":"sv-SE","EnglishName":"Swedish (Sweden)","DisplayName":"svenska (Sverige)"},{"Code":"th","EnglishName":"Thai","DisplayName":"ไทย"},{"Code":"zh-CN","EnglishName":"Chinese (Simplified, China)","DisplayName":"中文(中国)"},{"Code":"zh-HK","EnglishName":"Chinese (Traditional, Hong Kong SAR)","DisplayName":"中文(香港特別行政區)"},{"Code":"zh-TW","EnglishName":"Chinese (Traditional, Taiwan)","DisplayName":"中文(台灣)"}]
BrowserLocaleSupported : true
backendgroups : {"std":{"ftp":null,"ssh":null,"webdav":null,"openstack":"OpenStack Object Storage / Swift","s3":"S3 Kompatibel","aftp":"FTP (Alternativ)"},"local":{"file":null},"prop":{"s3":null,"azure":null,"googledrive":null,"onedrive":null,"onedrivev2":null,"sharepoint":null,"msgroup":null,"cloudfiles":null,"gcs":null,"openstack":null,"hubic":null,"b2":null,"mega":null,"box":null,"od4b":null,"mssp":null,"dropbox":null,"sia":null,"jottacloud":null,"rclone":null}}
GroupTypes : ["Lokaler Speicher","Standardprotokolle","Proprietär","Weitere"]
Backend-Module:

aftp

azure

b2

box

cloudfiles

dropbox

file

ftp

googledrive

gcs

hubic

jottacloud

mega

msgroup

onedrivev2

sharepoint

openstack

rclone

s3

od4b

mssp

sia

ssh

tahoe

webdav
Kompression:

zip

7z
Verschlüsselungen:

aes

gpg

Now it hangs. BackendSpeed is rising (584.35 KB/s). But the small File shown in CurrentFilename keeps the same.

**hmail Ext. Archiv-Ordner****:** 257 Dateien (0 bytes) zu erledigen at 584.35 KB/s

lastPgEvent : {"BackupID":"8","TaskID":4,"BackendAction":"Put","BackendPath":"ParallelUpload","BackendFileSize":6297099918,"BackendFileProgress":4925322055,"BackendSpeed":570966,"BackendIsBlocking":false,"CurrentFilename":"F:\\Backup\\hmail\\Data\\DATA\\archiv\\00\\{DATA-4671BC507D77}.eml"

Server Zustandseigenschaften

lastEventId : 78
lastDataUpdateId : 15
lastNotificationUpdateId : 4
estimatedPauseEnd : 0001-01-01T00:00:00
activeTask : {"Item1":4,"Item2":"8"}
programState : Running
lastErrorMessage :
connectionState : connected
xsfrerror : false
connectionAttemptTimer : 0
failedConnectionAttempts : 0
lastPgEvent : {"BackupID":"8","TaskID":4,"BackendAction":"Put","BackendPath":"ParallelUpload","BackendFileSize":6297099918,"BackendFileProgress":4925322055,"BackendSpeed":560768,"BackendIsBlocking":false,"CurrentFilename":"F:\\Backup\\hmail\\Data\\DATA\\archiv\\00\\{DATA-7539-463E-A657-4671BC507D77}.eml","CurrentFilesize":501730,"CurrentFileoffset":501730,"CurrentFilecomplete":true,"Phase":"Backup_ProcessingFiles","OverallProgress":0,"ProcessedFileCount":108019,"ProcessedFileSize":56267580094,"TotalFileCount":108276,"TotalFileSize":56267580094,"StillCounting":false}
updaterState : Waiting
updatedVersion :
updateReady : false
updateDownloadProgress : 0
proposedSchedule : [{"Item1":"2","Item2":"2020-05-26T17:00:00Z"},{"Item1":"3","Item2":"2020-05-26T17:00:00Z"},{"Item1":"8","Item2":"2020-05-26T21:00:00Z"}]
schedulerQueueIds : []
pauseTimeRemain : 0

Im wondering why there are 257 files with zero bytes and BackendSpeed is 584.35 KB/s. What is the backend dooing, while it blocks only one small file in the last 50minutes. And why is it showing 0 bytes. Is this a bug?