https://support.apple.com/en-us/HT203068
- iOS 8 and later search for SSIDs that have a signal strength/an RSSI of at least -63 dBm.
- They will stick to the same SSID until the signal exceeds -70 dBm.
- Then it looks for another SSID that is 8dB greater than the current.
If you are having issues with the connectivity please reach out to Support to check the connection strength at your location and we can troubleshoot further from there.