Transpires it is a known problem.
The link below may not jump to correct post. See message 2125
https://forum.openwrt.org/t/xiaomi-mi-router-4a-gigabit-edition-r4ag-r4a-gigabit-fully-supported-and-flashable-with-openwrtinvasion/36685/2125
Post dated 7 Feb 2022 suggests newer MT76 driver as of 31 Jan 2022 may resolve the problem.
https://bugs.openwrt.org/index.php?do=details&task_id=3989
May have to wait for next release of OpenWrt to get the newer driver if it is not already in use in daily snapshots.