Different issues during the dives

Bought the new Garmin MK3 Descent 8 weeks ago and just back from 3 weeks diving in the Tuscany - I did approx. 20 dives. Following issues happended during the different dives

Three times display got black during the dive and continued to get back to black after 5 seconds once I reactived it

Two dives had been lost after the dive - not on the log book ( computer worked during the dive )

One dive the computer showed 1,5 meter depth level on 22 meter depth after 20 minutes - 99 min no deco, no safety stop on 6 meter ( continued until the end of the dive )

On a 40 meter dive no deep stop had been showed - conservative setup

Unfortunately - this issues come and go - I have absolutely no idea how to deal with that. This never happended to me with my Aqualung or Suunto computers. Especially when I 

guide this is very uncomfortable - finally had for all dives my old Aqualung with me in addition.

Any ideas what the problem could be ? 

Thx