I have no idea if this is best forum to post to, but here goes:

The latest version of Excel for Android cannot reliably open old .xls files directly from OneDrive.   This problem started with the latest version released this week.  The problem was not present in the previous version.  I can still open .xlsx files directly from OneDrive, but not .xls. 

The problem starts with a strange message about needing to use Microsoft Secure online services or something like that, you then click Allow or Don't Allow.  After that the problem starts.

Now if I try to open a .xls file directly from OneDrive I get this message:

"Can't open file

Sorry, something went wrong and <file name>.xls can't open"

Now if I download the file and save it to the tablet, I can open it.  But this is not good enough.  I should be able to do what I could do last week, which was open them directly from OneDive and then close and re-save them back to OneDrive automatically. 

The exact same problem also exists in the new version of Word for Android, regarding not being able to open some .doc files.   .docx files continue to work reliably.

I have also replicated this fault at another site with different Android tablets, connected to a different OneDrive account, while opening different .xls files.  It's definitely not just me.

If I have posted this question/fault report in the wrong place, please let me know where I should post it.  Thanks.