I've had this problem frequently, and it seems to be a matter of the file being strained in how much it can import. File size doesn't strongly correlate with the problem as I have files of 18 MB that refresh just fine and files of only 9 MB that can't refresh automatically. But once I'm importing from ~6 or more Salesforce objects into a dataset, I'll start getting "Invalid Query Locator" errors sometimes when refreshing. Sometimes, these errors arise infrequently enough that reports will still continue to refresh most times. But once I use 8 or more Salesforce objects in one dataset, there's almost no chance that the report will ever refresh in the PBI service. I have end users who need to see information stored across this many objects for various projects, and we need a solution for this problem.