This is normal...while the data is refreshing, you cannot export reports. Just have them wait a little while and that should be resolved. If you need to kick it off, I usually go to my reports and (as an admin) and download any one...this will kick off the refresh process if it hadn't been done in at least 4 hours or less.

Yes. The datalake does do automatic refreshes now. But it can take sometime to process. I would suggest two things:

Express to the person that fact (that a reporting subsystem is refreshing itself with the latest and greatest data and it causes a pause at times based on load/performance).

It is typically not long. They should come back in a half-hour at most. That duration is probably safe enough for the datalake to refresh itself (well in our circumstances).