2.4GHz Wifi weird connections

Installing and Using OpenWrt
1

Linksys EA8500: router / Openwrt 25.12.0-rc1
Linksys MR8300: repeater bridge (relayd) / Openwrt 25.12.0-rc1
The wifi connection between the 2 is 2.4GHz
Both transmit to clients on 2.4 and 5GHz (4 different SSIDs)

The connection between the 2 (and sometimesr the repeater's 2.4GHz client) slows to a crawl, and the status of these connections shows something like:
6.5 Mbit/s, 20MHz, VHT-MCS 0, VHT-NSS 1
39 Mbit/s, 20MHz, MCS 10

I am not sure if 2.4GHz connections can be VHT.

When the connections are ok, they show up like 2.4GHz ones should.

Any idea what's going on?

2

Officially, no.

3

2.4 airtime is usually clogged heavily, just like non-DFS 5GHz, but even there 5GHz has 5x bandwidth, just try it if distance permits.

4

If you are using any usb3.0 devices on the router, it can interfere 2.4ghz