Not sure what you are doing, but you can drag midi from Reaper to an empty track in the BB Plugin.
The BB Plugin won't play back midi/audio to the DAW tempo map.
If you are using Reaper with Biab/Plugin you would be best to use this script it will transfer tracks instantly from Biab to Reaper and sync to the tempo map:

Originally Posted by musocity
Import-frozen-SGU-MGU-realtracks-drums-tracks-GUI.zip
This gives the great song generation power of Biab with professional editing.
Use this "Browse" button to set the path of the frozen SGU/MGU, this can be the SGU you are currently working on in Biab.
"Reaload Tracks" button will load all the currently frozen tracks in the SGU.
"Selected" button will transfer the track instantly into the selected track.
"New" button will transfer the track instantly into a new track.
"Set" button will set Reaper bpm to same as SGU.
"Import Chords" button will import the current SGU chords as regions (make sure to Unfold and save first), it will set the bpm and time signature.
If you update or add new tracks in Biab, just freeze the track and save, then simply hit the "Reload Tracks" button to update the track list.

EDIT: If you don't have the peak files already it will have to build them but once you have the reapeaks files it will be instant.
You can use Script: Create reapeaks in folder.lua

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