FLStudio'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 ...
FL 12 (e.g. a 64 bit plugin works fine on FL 12 64bit, a 32 bit plugin works fine on FL 12 32bit). I believe this issue occurred after a Windows 10 update, so Windows 10 itself [i:jik3jib0]may[/i:jik3jib0 ...