SOLVED: Help diagnosing a blank screen on mV range on BM257

[Bootalito]

UPDATE:
Ok, this is weird. I was watching this video   (calibration of another Brymen meter), linked from this post https://www.eevblog.com/forum/testgear/brymen-257s-lost-calibration-data/, and just for kicks I tried to initiate the calibration procedure for this other Brymen meter by pressing and holding the SELECT and HOLD button while turning it to Ohms range. It didn't actually go into calibration mode as this is a different meter.  BUT.  It suddenly works now!  I can't explain it.  I just held down SELECT and HOLD while moving the range switch to Ohms mode within 1 second and everything works now. 


ORIGINAL POST:
The mV range on my BM257 just has a blank screen.  Pressing any button doesn't do anything (typically SELECT switches to temperature; k-type thermocouple.  It just stays the same).  Long pressing the buttons makes a beep.  The LCD screen seems to be flickering on this mode whereas its rock steady on all other modes.  The battery voltage is fine.  All other features (V, ohms, diode, current, etc) work fine and actually seem to be in spec.
Anyone have any guesses or wild ideas?