A few suggested changes to your wireless config...
2.4 Ghz -
Use either channel 1, 6, or 11 (even in the EU).
Set channel width to HT20.
Transmit power can be set up to 25.
5 Ghz -
Take channel selection off auto and change the channel to one in the higher range that doesn't require DFS, In the US, I recommend starting at 153. Run iw list to see the non-DFS frequencies.
Set channel width to VHT80.
Transmit power can be set up to 30.
Both -
Set encryption to WPA2-PSK and AES.
I would also recommend Lizard Systems free WiFi Scanner to see what wireless traffic in your area looks like…
https://lizardsystems.com/wi-fi-scanner
If none of that helps, I would then suggest setting OpenWrt/LEDE to factory defaults, and re-configuring from scratch.