Halion se3 (Cubase artist 10) sudden soft sound

Using the (standard) Halion in Cubase artist 10 causes a problem. Sound of the instruments will quite often dim. Sometimes after a chord or 2, sometimes after a couple of minutes.
We couldn’t find any strange CC messages in the list editor, neither is the meter ‘audio processor load’ showing any problem. Buffers are ok.
Softening the volume of a sound in Halion has no advantage anyway …
Anyone same experience? Solution…?

Thanks in advance!