I had this issue and managed to find a way around it, but I thought it was worth posting. I’m still not sure if I’m the only one.
The first issue occured when I tried to use the automatic sync button. A message appeared saying that ‘this file doesn’t belong to any existing project’ (I double checked to make sure that I was logged in and I was). So, then I tried to search for the project manually and use the sync button there. That worked, but I was only able to sync the new data output files from the online repository. The changes I have made to the .js and .psyexp files were not committed. In other words, the problem was isolated to modified files only and not newly created ones.
I managed to get around this issue by committing the files manually using cmd. Using ‘git status’ commands I was able to detect the modified files, and then add, commit and push them to pavlovia successfully.