I found a way to reliably reproduce it. It appears to me as a bug/malfunctioning of the Flows API server.

It's very important to notice that same symptoms also frequently reproduce, even if WhatsApp stays in foreground.

Best to be reproduced with iOS.

1. Click a UI component which has a data-exchange action
2. My server gives a very fast response to the request, in a couple of milliseconds (I see that in my logs)
3. Open the iOS app switch quickly (swipe from bottom to top) and select another app
4. WhatsApp backgrounds
5. WhatsApp has now 10 seconds left to finish any pending operation, such as the pending network request for the data-exchange action
6. Wait at least 10 seconds in your other app
7. Navigate back to WhatsApp and notice the "Type Error / Load Failed." screen.

Again, because the reproduction is an edge case, BUT the same symptoms also occur frequently while WhatsApp stays in foreground:

The problem seems to be with the Flows API which is supposed to give a server response back to the WhatsApp client app. But either it times out (as presumably described above) or it returns an error. As the WhatsApp client app doesn't give any other details, I can only speculate about the reasons here. But it seems evident that the meta Whatsapp Flow API server is misbehaving here.

To my opinion the WhatsApp client should NOT navigate away from the current screen to this error screen. Instead it should show a regular flow error toast at the bottom of the screen, asking the user to try again.

And I just had another case of that "TypeError / Load Failed." screen, likely with another root cause however. It appeared instantaneously when I clicked a drop down item with a data-exchange action. There didn't seem to have any network communication happened at all, given the screen showed instantaneous. My assumption is a network connection error client side in WhatsApp itself.

I suggest to add request retry logic to all client-server communication in flows in case it's not yet implemented to provide a better UX to WhatsApp Flows users.