“Make available offline” file status is changing on its own on the mobile app

I have a folder with 600+ files in it.  I check the status of every file “Make available offline”. These are song lyrics that I need in live shows.   Tonight 80% of them suddenly had the ‘yellow triangle icon with exclamation point’ icon showing which means they were NOT available to me. This is a nightmare!!   
pluckily I was able to jump on Wi-Fi and access a few (but not all) of them. 
I just sat at home and went thru the list and re-marked each one to be available offline. Closed the app. Reopened and 20-30% had reverted back to having the yellow icon.  Some changed from green to yellow right before my eyes, for no apparent reason.  I’m at a loss as to what to do.  Help! 
I have not changed anything EXCEPT I emptied cache yesterday, because I was advised in the forum to do this, to deal with the (different) problem of the alphabet tab disappearing from the index (ANOTHER NIGHTMARE, apparently a known programming change).  Could emptying the cache have done this? What can I do? 
The entire file index list has become unstable, and EXTREMELY tedious to use without the alphabet tabs. It is changing on its own, and not doing what I’ve told it to do. 
I’ve used Dropbox for 10 years+ with no major issues like this. 
Can you guys fix this PLEASE PLEASE PLEASE.

thank you.