I'm just following up on this - it's been a few weeks and you hadn't gotten a response, a key reason why is that without seeing your data and the flow it's really hard to help. See Packaged workbooks and flows: when, why, how for more info. Unless one of the volunteers here has seen the exact error (personally, I haven't) we can't really help.
Also I can see in the version information that you're using Prep 2019.3, which as of this writing is still in beta. In that case I'd definitely recommend that you reach out to Tableau on the pre-release site because you might be using a new feature that isn't in general release yet. Otherwise I'd be suggesting that you reach out to Tableau technical support.