VST2 multchannel numChannelsChanged don't get called

I have a multichanelpugin and when trying the VST2 version of the plugin with the host reaper it is always identified as stereo.

It is something wrong with my VST2 implementation of the plugin because numChannelsChanged() never gets called when VST2 but in the VST3 version works as expected.
What could be the problem here?