I have had this issue where I normally connect by USB to my iPad from my Mac and try and transfer photo folders from an album - on installing Catalina I found like others nothing synched and the existing folders on my iPad were wiped off.
I have just finished my third call in a week from an Apple Tech who has finally declared to me on this occasion that this is a 'known problem and they are working on it" - basically watch this space for an upgrade.
Meanwhile he offered me this temporary solution that works(for me) -
Connect your iPad and Mac together,
Go to Photos,
Select a sub folder
Choose - 'File' - 'Export' - 'export album' - export'.
Go to Finder
Your folder from 'photos' is divided into the dates the photos were taken will be listed in 'Downloads',
Then -
On the iPad page select the 'photos' tab,
Where it says 'synch photos to your device from -' select from the dropdown 'choose folder',
Select - 'folder' , choose one of the dates folders - 'open' - 'apply',
By some miracle the photos should transfer to your iPad - they did on mine.
Its not the best but you can by this move photos across albeit not in an album format,
hope this helps someone