Adding and readding devices failure

[PeterHa]

Yes there is a limit, have a look to this thread…

[HOW TO] Plan and setup your Zigbee network

This post is concerning The order of adding Zigbee devices to your Homey Pro/Bridge (AKA “Coordinator” or “hub”). Know that there is a best approach to in which order you connect your devices. You have at least three major category of devices. Which to connect when, that’s what I will dive into in this article. What are the issues? So, cutting right to the chase: The most common issues you will run into with your zigbee devices, is either unreachable devices or you’ve added the maximum of devi…

I’m using also the Sonoff temoerature sensor, and I had no problems with the installation.
Have you tried to restart the Sonoff-App and/or to restart the HP23?