We’ve identified one of the bigger bugs causing these sorts of errors so will soon be bringing out a bug fix release which should allow you to sync as normal!
In the meantime, one thing which might help is if you go to your user folder and delete the file projects.json in the pavlovia folder. The location of your user folder is different on different operating systems, but an easy way to get there is to go Themes → Open Themes Folder and then go up one folder, as the themes folder is inside your user folder. Once the projects.json file is deleted, so too will be the reference to your old study ID and so PsychoPy should then be able to pick up the new ID from the local git folder.