and am wondering if this is the cause and the solution of my problem. Would a DBI/mysql savvy monk kindly elucidate?

That would seem to be the cause of your problems -- turning on this async feature, means you have to wait after execute before you can fetch

So the solution would be to comb your code (or whatever abstraction you're using), to make sure async is turned off

Or add the loop as per async docs, to wait before fetching