Sorry, that I forgot this information.
I sync over local network only.
I use DEVONthink Server on my Mac (still Monterey). On the iPad Pro (still iPadOS 16.6) DT To Go, both in the current version.
I use both machines for every day work - half of the day the iPad on the go, at home the Mac (iPad for private on the couch ;-)). When sitting at the Mac I turn on the iPad and sync locally.
When the described behavior happened, no sync was running, the Mac in the local network was turned off.
On the iPad I often send webarchives from the browser over „sharing“ to DEVONthinks inbox for remembering, reading later and deleting, saving for certain things etc… When I open DTTG later, it shows me, that it is importing the objects, indexing it etc. - takes just a few seconds to finish. Last time it starts the same way but repeated it again and again with the same „new“ webarchives from the „waiting-for-inbox-list“, putting more and more duplicates of them in the inbox.