This happened to me about a year ago…
I tried a lot of troubleshooting, but could never resolve it. I switched to Lexicon DJ and it’s been smooth sailing ever since.
There are a few caveats. I don’t use Engine DJ stems and I do all the prep in Lexicon DJ. I sync to the performance USB drives directly from Lexicon DJ. This process has also made it easy to sync to other software.
I bought an annual license to LDJ with a coupon code from Crossfader. LDJ started offering lifetime plans several months in and I was credited for the remaining time and switched to lifetime. The software is progressing regularly. The owner/developer, @Christiaan, is ever present on the discussion board and responsive.
BTW, when I sync to the EDJ USB I have the Smartlists converted to regular playlists.