@rotbot Make sure your wireless settings for both bands are: For 5 GHz band you can set Mode to 802.11n/ac mixed. The other thing you could do is to scan the spectrum with an app like Wi-Fi Analyzer...

@itsMHmoon Here - the top one.

@mfran2002 Update both APs FW to the latest one available and see if that will improve the operation in wireless repeater mode.

@mfran2002 What if you set the floor 1 device as AP and its SSID the same as the ground floor's AP SSID.

@RocTaiwan It's quite possible that this device has dual network adapter, so probably if you block the second MAC address as well, then the device won't connect again with a different MAC address....

@Soumya179 Check the sticker on the bottom of your device to see for which region (EU, US, RU) and HW version it is. Then download the FW for that region and HW version from the support site.