Since the current built-in way to access Mega by Duplicati doesn´t really works for everyone, it might worth look into the usage of MEGAcmd, which is the recommended way for that…
I just received the below email form Mega´s support:
Thank you for your support and for using MEGA!
It looks like you are using some kind of third-party tool. Please exit it in order to rule out a possible connection between this program and your ongoing issue.
You can also exit it by going to your MEGA account session history and click “LOGOUT” on those “Unknown”/“Linux” sessions.
Please note that these tools are insecure and do not fully implement our cryptographic protocols, therefore if you cannot access your account, that could be the reason.
If it is the case, you must use one of our official tools (MEGAsync, MEGA CMD, mobile apps or MEGA in browser) to unlock your account.
You will have to wait 30 minutes after log in for your account to be unblocked.
We do not recommend any third-party tools. Our onsite download is already using multichannel downloading. The Internet Download Manager, JDownloader or any other third party download client have not been approved or authorized by MEGA and should only be used at your own risk.
Also, these foreign tools cannot detect your quota and could limit your bandwidth.
To manage your transfers, the best way is to use MEGAsync - our desktop sync and download/upload client. It can be downloaded here: MEGA Desktop App - MEGA
From MEGAsync interface, click on the top-right menu and select “Open links” from the dropped-down list.
If you are not using any third party tool and you are concerned about the security of your account, please check here What should I do if I notice suspicious login activity on my account? to find out what steps you can take.