I had the exact same problem since switching to the newest version. Even after switching back to 2020.1.3 I were not able to synch my paradigms again.
In my case the the TextBox component caused the problem and this was my workaround:
My text was: $cue + " = " + $target
I added a Code component and created a variable at the beginning of the routine: itemText = cue + " = " + target (same code for js) and used the variable in the TextBox text-field.
The errors disappeared and I was able to synch again!
You could also share the link to your project, or upload the psyexp-file. Then I can have a look at your experiment.
Apologies for my really late response! Thank you for your suggestions.
Somehow it seemed to resolved itself. What I did end up doing was rebuilding my experiments in the newer version and it seems now that it is okay (fingers crossed).
Hopefully the issue won’t return but i will keep your advice in mind for the future