I have this issue whenever there is a big Synology update. I check the package manager and it usually says Duplicati is NOT running. But if I ssh to the Snynology and “ps ax” I’ll see it running. I kill the process and start it again using the package manager and all is well. (Until the next major update.)
I have a feeling it may be a flaw in the Duplicati package design. I don’t have this problem with any other Synology packages.