On the latest firmware, over a period of time (typically at least 12+ hours) devices connected to the 2.4Ghz band experience slowness. Household members and myself have only noticed since the 1.1.3 update (from the prior 1.1.1 build) and the only setting change after upgrading to 1.1.3 was re-enabling OFDMA+MU-MIMO

All of my band SSIDs are separated (i.e. Wifi2/5/6 SSID names) -- all band modes are capped at AX mixed level (or equivalent)

Changing the 2.4Ghz channel (i.e. from 11 to 6) will restore expected performance and no reboot is required. Other bands do not experience this issue. Rebooting the router without changing the 2.4Ghz channel will also restore expected performance.

I assume it's a bug/issue with the 1.1.3 firmware since the only thing that has changed in my setup post-upgrade was restoring the OFDMA+MU-MIMO selection from OFDMA only.