Hi Witzker,
i got stuck on upgrade from 16.0.5 to 17.0.1 too. Verification failed here:
Got “Message: Signature of update is not valid” and “Message: Not exact 3 files existent in folder”
Reason: Updater expects only latest zip file in download folder with correct signature.
Solution:
Read end of updater.log and find out download path, mine was /volume1/Nextcloud/updater-oc2mk9t8au24/downloads on Synology. Go to this path on Nextcloud server and check out what is there, write down file permissions, mine was rw-r–r-- http:http
Download latest (17.0.1) [nextcloud-17.0.1.zip] from https://download.nextcloud.com/server/releases/ by hand and place it to this folder delete/move the old one so only the latest zip file is in download folder nothing else.
click retry update