I think it may be the same problem I report in my post when testing 4.2 snapshot firmware in my AR750S. I will try again in a few days
Firmware openwrt-ar750s-4.2.0-1219-1671403982 in a AR750S
Here.
https://forum.gl-inet.com/t/ar750s-new-snapshot-4-2-x-firmware-available-testing-here/25868/6?u=david