So far I've tested the VST3 vs VST2 versions of Fabfilter Pro-Q3 and Pro-Q2. In both cases, the VST3 version will visually seem like it's working (at first), but it's not processing the sound in any way. By contrast, the VST2 version is working fine.
I am on the latest 3.11 release of all FabFilter plugins.
This was tested in Bitwig Studio 2.5 and 2.5.1 RC4.
I wonder if this is related to the similar problem reported by another user here about 3.11 VST3 not working in Digital Performer 10?
FWIW, all earlier versions of your plugs had the VST3 instances working just fine in Bitwig 2.5 and 2.5.1 betas.