Getting 'Export Failed' while downloading data in xls format

I am struggling with that error message, too (Export Failure), and thought, I have found the right thread here. However, I fail to understand how to download (for comparison) the various xlsforms used over time in this project (“Download your xlsform (different deployed versions) by cloning them.”). Can you please help?

Anyway, I am almost 100% sure that I haven’t changed any repeats. What else is a typical source for export failure?