Nextcloud issues after updating router

I am sorry, but if you are seeking for any official response from our team, you should start with Getting help article as a forum is a place, where the community helps each other.

Cross-post from your thread, which you mention:

Can you check if your external storage is mounted correctly? Are you using USB flash disk drive or HDD/SSD? Were they plugged during the update? This is important. If it gets unmounted somehow, then the update of Nextcloud goes proceed on eMMC, which is not wanted.

And this is the issue at all. Nextcloud does not provide support and they don’t even suggest it to skip major versions of Nextcloud. You should be following it one by one and this is what we are currently doing in minor Turris OS releases.