If you don't need Airplay2 specifically, load DietPi on a RPiAre there any other quality streamers that do Airplay bitperfect at 44.1khz? I only know of the Belkin (but that upsamples to 48k?) and streamer-dac combos (no clue on output, but cost goes up with features i dont want)
But for the issues you are having, return your WiiM Mini for another unit.
If another unit has issues , it's your WiFi.
My WiiM Mini and Airport Express run flawlessly with Airplay2 (ethernet for the AE)