Hello all! So after a month of headache I have finally found the issue causing one of my reports to "break" when refreshing online. Everything looked as it should and refreshed correctly in desktop, but the refreshes online turned up differently. The problem is the data source I am querying from (Business Central) outputs 1/1/0001 in place of blank dates. Desktop reads these and displays them as blank values, so DAX expressions using "ISBLANK()" work on them. However, the web service does not read these as blank so these measures did the opposite of what their intent was. Would be great to make the treatment of 1/1/0001 consistent across both platforms to avoid future confusion. Thanks!
Update: Steps to recreate
Enter data with a 1/1/0001:
Change type to date:
Close and apply:
Create a measure using some form of "ISBLANK()":
Resulting measure differs from desktop version:
While I get there is a super easy one-line fix (adding a replace 1/1/0001 with "null" step in power query) the issue is for users who encounter this but don't know what the problem is (like me). I think in general the expectation is that if I load something in desktop, this is how it will load online, and it is very confusing when it doesn't.