Wifi network goes crazy after hass.io restore on RPi with SSD

After over a year running HA on RPi 3B+ using SD Card on wifi, my sd card died and I moved to SSD.

During the the hass.io image installation on the SSD I had the RPi connected to my LAN. When done, I restored a snapshot I had. Afer that, I upgraded to latest HA version. Then I connected a USB flash drive named CONFIG with the “\network\my-network” file as was working with previous sd card and rebooted.
After restart, things started to go wrong -

  1. I couldn’t access the HA portal using the saved IP (I have my router allocating saved IPs by MAC).
  2. When connected LAN again - I could access the HA portal as usual, but while the RPi was running, all other wifi devices on my network (like phones and laptops) started to get difficulties with connection to the internet. Either the wifi router (using DECO M5 mesh) refused to connect them or they could connect but didn’t receive internet. Sometimes, some of them could connect normally and them lost it again. The network restored to normal operation once I shutdown the RPi.

Now I’m not sure what can I do. I don’t even know where to start looking for the problem…

Any help will be much appreciated!