Had an issue yesterday when trying to install a dimmer2 at my parents home. Been using it at my home before that but over mqtt and with openhab (so I don't think cloud was enabled when I started the process but not totally sure). The problem was that the dimmer2 was on my shelly cloud account and then could not be at my parents in the same time, totally logic and my own fault (!) but the IOS-app never helped me understand that.
The story: as short as i can describe it, with my solution.
First: I did a reset (10s press on physical button on the unit) and then tried to add it in a LOT of ways to my parents new shelly account. I got it connected to wifi and it got IP etc. I was on the same wifi and it was a 2,4ghz wifi.
Tried with different IOS units (12promax, ipad, iphone 8 etc).
I tried both with DHCP and static IP. It always worked like a dream if I connected to it through a browser with it's IP but in the app it was very difficult with a lot of error messages that did not help me so much (like connection lost, this device has not reached the cloud yet..., you need to be in the same wifi...)
My problem was that i couldn't turn "cloud" on in the app. not in the installation process noor afterwards in the app. If I connected with my computer to the IP adress I could turn cloud on and off but doing so never showed cloud on in the app. I also tried on my parents standard network you get from the ISP and my home Ubiquiti-Unifi network with the same result. And I also tried to add it in all possible ways in the app. I could add it without cloud but then it worked really poor in the app. (over IP everything always worked very well)
After quite some hours I tried with an old android. That phone told me with an error message that my dimmer2 was connected to an other account/cloud. So after that it was easy, hooked it up with my personal account again, made sure cloud was disabled and after that did a factory reset through the app. And then connected it to my parents account with shelly cloud set to on on first attemp.
So there is some kind of bug here in the IOS app. If anyone needs more info about this matter I'll gladly help!