When uploading a newer version of the zip file (with the same names inside) students reported that it doesn't seem to actually overwrite the old submission. (doesn't actually upload).
I am unable to reproduce this. I uploaded a zip, made some small changes to the files and uploaded it again (with the same zip file name) and it clearly showed the new timestamps (the new files were uploaded).
When uploading a newer version of the zip file (with the same names inside) students reported that it doesn't seem to actually overwrite the old submission. (doesn't actually upload).
Check if this can be reproduced!