Problem with motion blur

Experienced a strange issue with two of my project.

Renderers Motion Blur option is only effecting the very first frame of my composing.
Other times in different projects the function works proper.

Anyone with an idea what could be the problem here?
I am running Fusion 9 (the free version) on WinX 64bit.

Thanks.

without any examples just the obivous questions:
are the objects and/or camera animated so that motion blur can be seen?
is motion blur turned on? in the viewer? in the rendering? in the nodes?
is it animated? (on/off/amount)

Yeahr. It's switched on in the renderer-node and also for the preview (MB-Button) And I do see the effect in the very first frame of the project. I can even render out and save that frame as a picture or into a .mov. .avi etc. But it disappears directly from frame 2 on for the whole rest of the composing. Always only one frame is processed with the renderer-notes motionblur. :/

Try to disable OpenCL in the Preferences and see if i makes a difference.