The upcoming OpenWrt 21.02.2 release will include the fix by @nbd.
Get the OpenWrt 21.02 snapshot images which include the fix:
I use Linksys WRT32X as my main drive. Wireless is unstable on OpenWrt 21.02.1. Wi-Fi client does not disconnect but it won't receive/transmit any data for a minute or so. This happens regularly.
I had no issues with OpenWrt 19.07.7.