EDIT: please also check this thread, seems to be about the same problem:
EDIT2: and especially this one, near the end:
There’s mention of an updated mediatek firmware that should seemingly fix the problem, but its availability depends on your distro.
In the distro I use, opensuse tumbleweed, mediatek firmware files are under /lib/firmware/mediatek, and I saw that I have the fixed version installed: WIFI_MT7961_patch_mcu_1_2_hdr.bin.xz