That sounds like you’ve gone through all the steps I would suggest for diagnosing the meter, really sorry for the trouble.
Just making sure I understand: the pattern you’re seeing is 2 long slow blinks, 2 quick blinks, a few seconds of delay, then repeat from the beginning? Or is it 2 long slow blinks, 2 quick blinks, then just an occasional blink?
If it’s the latter, the meter might have reset to shipping mode somehow, try waking it up by shorting the Ω and C inputs together for 10 seconds or so.
One more question/thing to try: Is there an SD card in the meter? If so can you try removing and seeing if the behavior changes? Kind of a long shot but I’ve seen defective SD cards cause reboot loops.
If none of those are the case, I think you’ve done your due diligence so we’ll happily exchange the unit. This is the second unit we’ve heard of misbehaving after 6 months in the field so it’s important to us to get them back and understand any latent issues so we can address them.
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Sorry again for the trouble, thank you!