Vario Problems

My glider is equipped with L-NAV/GPS-NAV. Over the past weeks I have
noticed some problems with the vario. For example it gets stuck and
shows constant lift (visual and audio). Turning the instrument on/off
does not help. Slapping the instrument panel has helped. That makes
me think it is a connection problem of some sort.
On the last flight I noticed that the total energy compensation does
not work. Using my old trusted hang gilding vario (uncompensated) I
noticed that both showed nearly similar lift. Needless to say, that I
turned quite a bit in sink.

Any ideas/suggestions? Your help is appreciated.

Thx. Johann