Wavelab 9.5 playback counter and waveform speed

Recently, WL9.5 has been acting strange from time to time.
the playback counter (nibutes, sec etc) is counting, but a second is taking like 2,5 seconds
at the same time, playback position in the awaveform is massively behind.
playback is fine, but when the track ends, the playback position is like 25% into the file.

What to do?

Windows, prism Lyra, 512 or 1024 buffer