Just to let you know, this is a problem that exists for years, and never got fixed.
Also it is not related to how often you use it, more likely its related to how many Devices you use.
In my Case
2 Windows PCs
2 iPhones
1 iPad
1 Linux Notebook
It takes one to two weeks until Enpass asks for a password to reconnect.
Neither the the Database Password nor the Nextcloud Password is accepted.
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There is no Fix to it, and only a Workaround.
Workaround:
Disconnect one device from the Sync.
Make a Backup
Delete Data in the cloud.
Reconnect the device to the Nextcloud instance.
And all previously connected devices stop complaining, and sync works as intended again
After a week or two rinse and repeat.
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Usually people complain about it, and nothing happens.
People have accepted, the workaround or moved on to an alternative.
I was part of the first group, but since Enpass is now nagging you for a subscription.
I will join the later.
God Speed