I’ve had similar issues since early last week where files were downloading with incorrect file extensions - causing them to not open correctly. Most of our issues have been resolved though, with the exception of Excel .xlsm files which are still downloading as .xlsx.
Not sure if your issues fall under the same category as ours, but I’ve been communicating with the support team back and forth on this and we’re almost 100% resolved. The team has been really great at working through all of our file issues, so I would suggest emailing firstname.lastname@example.org.
Hope that helps.