[tomsem]

FWIW I do not think it is necessary any more to restore covers (on Kindles with the sync-system-time update).

I have tried everything I can think of to let it happen, and it just doesn't. I think update that delivered the system time synchronization feature was responsible for this change, and lack of time sync is/was responsible for flagging thumbnails as 'remove and try to update' as part of sync (consistent with use case of side loading AZW3 downloaded from Amazon, where it will sync any annotations, download X-ray info, cover thumbnail, etc).

So if there were some option to disable the extra work calibre does to restore thumbnails on Kindles, I would use it (older Kindles probably still need it, I'm guessing).

I also tried to reproduce @RKrueger's issue and could not, at least with as many as 350 books on the Scribe (I let it sit around to finish indexing content before testing). It never took longer than about a minute for calibre to finish its sync (including whatever the polling period is for checking for connected devices). And with my usual 20 or so on device, less than 30 seconds.

I don't consider this particularly slow compared to USB MS, which can take awhile just to mount on the file system (it takes less than 5 seconds for Scribe and Android devices to go into connected mode).

File transfers are also not slower and often faster when I have tested Scribe and compared it to Paperwhite w/USB-C.

Which is not to say I think the change to MTP was particularly merited or welcome.