If the Shelly devices that you are trying to re-add have connection issues with Homey it’s likely these connection issues are also present during device discovery and your devices are not discovered. What happens if you manually try to add these devices in my app (this option is given in the paiing wizard if no devices are found during pairing).
If you really want to look into this further you can try and run the app from the command line using this tutorial. It will spit out extra logging on the command line when the app is run using the homey app run command.
