Catalina (10.15.1 (19B88)) USB drive terribly slow and unstable

I recently upgraded to Catalina on both my Macbook Pro 2014, and Macbook 12'.

Photos export to USB flash drive doesn't seem to work securely.

1. It's extremely slow. Export (drag and drop) iphone 7 .heic .mov, .jpg files 200s takes more than 30mins to complete. I've tried multiple flash drives, including reformatting into exFAT. All USB drives I tested works 100% OK on Linux, Windows, same machine in Mojave. I have tried rebooting system.
2. Photos export to local drive seems normal but copy is then same slow.
3. Sometimes, after Photos export, files don't show up in the Finder. Although folder properties shows the right number of files in there, but file list pane is empty. I have to replug to see files. (But exFAT, and FAT)
4. I don't have hard evidence. But I have a feeling there are missing photos in my libraries, I will have to use time machine to search.

Please test and fix in future releases, otherwise I have to roll back to mojave.

Regards,