VP9 message in jvb.log

I see this a few thousand times in the jvb.log

 Vp9QualityFilter.doAcceptFrame#231: Want to forward E0S2T0 frame, but can't! layers=true, true, false, false, false, false, false, false, currentIndex=E0S2T0, isInterPicturePredicted=true, usesInterLayerDependency=false.

Does it just mean some participant can’t handle VP9, or is it something serious?