FL Studio's plugin manager is not up to date with the latest versions of the SDK.
This was taken from the page "VST 3 Locations / Format" in the SDK documentation:
[quote]
On the Windows platform a VST 3 Plug ...
forum FL Studio 10.
I installed Wavesfactory Trackspacer2 (on Windows7 64bit).
I Installed VST2.4 (32bit) and VST3 (32bit and 64bit) of that plugin.
I opened FL Studio 10, and after I scanned for new plugins(a few times) only the VST2.4 ...
forum Thought it was a bug with the WaveShell at first but Auto-tune EFX 3 (which is only offered in VST3 format) also reverts back to its default state when re-opening a project.
macOS Sierra 10.12.5
FL Studio Beta Candidate 1.41 ...
forum FL Studio 20.1.1 and VST3 instruments. If I play a note very softly, or manually set the velocity to 1% in the piano roll, the note is completely silent. This happens regardless of velocity routing inside the VST3 plugin itself ...
forum