Check your experiment name
The experiment name is in Experiment Settings
When you save a new experiment, this name gets set as the name of the psyexp file (minus the psyexp extension). However, if you create use an existing experiment to create a new one, it will still have the name of the original psyexp file. In some versions of PsychoPy this can cause issues if you try to run the experiment online. The new JavaScript files have the same name as the psyexp file but the indel.html is set to load JS files with the old name. Update the Experiment Name in Experiment Settings and resync to solve the issue.