First "Move" after startup jumps to Y:420 (just the indicator, not the laser)

Found this Belt skip and jumping machine when FRAME is selected - #3 by Sunwriter
but a little scared to type in $RST=$, without knowing what I’m doin.

I used this machine when I first got it and it didn’t have this issue, so maybe resetting the firmware will fix it.
I got this a month ago then couldn’t play with it anymore until now.
I did have to unplug it a few times while it was trying to home in the wrong direction maxing out. and skipping steps.