The following worked for me: Booting memtest86, going to config>settings (same as pressing ‘e’ key)>resolution 2256x1504. I’m on on BIOS v3.06. I found that setting resolution to 2256x1504 at least centered the output on the screen for me.
Also saw the same thread by passmark as the one mentioned in the post I’m quoting. Is this a firmware bug we have to worry about if booting other operating systems?