I have the same problem with my 5 mooshimeters with last firmware upgrade, trying new batteries or lithium ones but no way to solve the problem.
I sent emails to James, to the support, but they never gave any reply. Only people on the forum replied but that was not satisfying at all and my problem is not solved yet, so I am actually working with other meters as my research project fell down because of this.
It seems that the support was very efficient at the beginning and now this is only the users community which provides help…
But we never know maybe you will be more lucky than me!