Some of these came preinstalled with malware. Besides that, try it wired for a test run.
https://www.asus.com/us/Mini-PCs/VivoPC_VM42/ notes it has a 5GHz channel so test with that as well.
I have an ASUS VM42 Mini-PC that has an extremely weak wifi signal. I purchased an external wifi adapter too and it did not resolve my issue with wifi reception.
My laptop and phone both get a full 35mbps from right near the computer when it's off. Their wifi speeds also plummet the moment the ASUS is switched on, so obviously this mini-pc is releasing some crazy interference that's blocking wifi connections in the room.
I shielded the external antenna with some aluminum foil and it brought speeds up from 100kbps to 7mbps and the signal isn't dropping out, but it's still much slower than it's supposed to be.
What could cause such massive wifi interference within the Mini-PC?

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