Cannot Save Changes Made to Xcel File Saved in DropBox Using iPad Pro 12.3.1 iOS

I keep my financial budget in an Xcel spreadsheet that I update with changes each month. Recently I have begun experiencing issues trying to save updates to my file. All my files are “stored” in DropBox account (not on iPad); open files from Xcel app on iPad Pro 12.3.1 iOS, make changes, and either Xcel will crash, losing all my changes, or I’m told there is some problem, cannot save changes, save copy of file, or try again later). This is has been going on for weeks now. Microsoft seems to think it is an issue with DropBox. 

Everything worked as it should until just recently. I have updated the iOS on my iPad, and Xcel app is up-to-date. I don’t know if a recent update has affected how Xcel works with DropBox and/or whether I have settings that have “jumped off” some way. Have read some similar difficulties in forum. Some show “Solution”, but when I go into read WHAT the solution was, nothing useful is found there.

Can someone help with this issue please? What changed from an otherwise “well-oiled machine” of a record-keeping system?