!! Dive never started !!

The dive mode never started for my 13th dive with the Descent MK1. I surfaced and tried again but it would not start. I continued to go deep and at first I had the gauge actives so I could see how deep I was going. After several minutes in the near 39m, the gauge suddenly began ton indicate between -0,2m and +0,1m... whatever the real depth I were....
the dive has not been recorded either.
Anybody experienced such one ????
It is scary.
In the afternoon I did not experienced the same issue. The dive activated automatically.