I have been fighting with trying to determine why ChromeHeadless export is giving me an Exception "Could not save content to temporary folder". After much debug I finally discovered it has nothing to do with permissions at all.

At the point in Exporter.php around line 239 where it is attempting to perform a file_put_contents the contents in my case is empty so the function is returning 0 bytes written which is being interpreted as false and throwing the exception.

There really should be a test prior to the file_put_contents for empty content and throw an exception on this so the error condition reported will more accurately reflect the actual error.