There are always a lot of conversations around grbl losing it’s mind and frequently it ends up being down to EMI from the router. Thankfully, as the kids say “I got 99 problems, but EMI ain’t one”. I’ve never had this issue on mine and while I’m sure there is more than one reason for this, I’m applying a certain amount of credit to the fact that my S3’s power supply is running through a voltage conditioner.
I use a bigger one (because I had it already), but something like this should be more than adequate: http://a.co/7P3CvlH
I use them on any possibly sensitive electronics around here, as our power in rural NC is generated by a hamster on a wheel, cow farts and the dreams of hippies. Note that these are quite different from a surge protector. These will boost or buck incoming line voltage (within a range) and deliver clean, noise-free power to whatever is plugged into them.
$50 isn’t a bad test if you’re having bad EMI problems. If for no other reason than testing to rule it out.