Perfect, thank you!
I have a possible clue. There are two suspicious lines, where the plugin tries to create it’s directories within the cache folder. My guess is that it may fail with the default permissions and defaults back to the lower ones.
Is it possible to get temporary FTP access to your site? I would try to modify those two lines directly, then you could test it afterwards to see if it the error disappears. If so, then I can include the change in the upcoming patch.