I'm having issues with running flow to output in my Tableau Prep file. It fails with all output types (hyper, tde and csv). My file is 4 fields and 555K rows, which doesn't seem all that large to me. Excel can handle this large a file but Prep is having issues. Not sure where to go from here. The error message isn't all that detailed.
You might have to get in touch with Support, it's hard to tell from the screenshot and the error doesn't actually tell you anything at all (like you said).
If it's possible, can you attach the files & workflow ? But please don't send confidential data, randomise the data first.