@volker I don’t know at what scale you’re shipping out products, but I do this: Photon WiFi at customer site - successful provision, but never moves past flashing green - #21 by policenauts
If you’re working at scale this is obviously not realistic, but after having one too many WiFi connection failures during customer setup, I now send along one of these TP Link units with each Photon-based product I sell and pre-provision the Photon’s WiFi credentials to that TP Link unit (which obviously takes time). The customer then doesn’t even need to do any WiFi provisioning at their site, I instruct them to simply plug the TP Link into the back of their router and they’re immediately connected.
If you take the above approach, one thing you could do (which I’m now going to do, going forward) is you also modify the password of the TP Link unit to make them all consistent, so that if their TP Link access point fails, they can simply order another one, modify the settings and password themselves, and in theory the Particle WiFi product should then connect to the new one.