Using the plug-in (latest version) in Reaper (latest version) I'm running into a few issues. After opening a file, selecting a bar then selecting "Bar Settings" or "Song Settings" toward the top right of the screen, the settings dialog floating window was showing up on my 2nd monitor, which I did not have turned on. Every time I open the bar or song settings the floating window is on my 2nd monitor (which is now turned on).
The first time, when my 2nd monitor was off I thought it was a bug given the rotating icon in the plugin that never stopped. While this might be a Reaper bug, when I went to close the FX dialog window, while the settings dialog was unknowingly on my 2nd monitor, Reaper crashed.
I had never used the plugin in Reaper so I'm not sure why the settings dialog would show up on the 2nd monitor to begin with.
(Windows 10)

Tried to help and when I hit the "settings" button in the BIAB-VST, Reaper crashed.
Others are reporting the the VST3 is a problem in current BIAB-VST with multiple DAWs. I would suggest you try the VST2 - except.... I was just running Reaper with the BIAB-VST3 and it was working fine. Then when I tried to reproduce you report, it crashed as soon as I hit the "settings" button.

Sorry, not much else I can suggest at this time other than to suggest the menus and windows which open in the BIAB-VST should remember where and on which monitor they were saved.

I didn't even install the VST2 version. Except for the dialogs showing up on the other monitor I guess I'm having better luck than others. The VST3 plugin is working fine, so far, except for the monitor issue. I usually use BB as a stand-alone but thought I'd do more with it in Reaper.

What monitor is set to "Primary" in the Win display settings ?

If the one marked "1" in the win display settings is the primary display then it is the monitor where I was looking at the main BB screen (chord chart view). The dialog box showed up on monitor 2. I use extended display in the settings.

Do the other windows go to monitor 2 like RT Picker, Drum Picker and Style Picker or just the 2 you mentioned ?

Thank you for the feedback James! I will pass this along to the BIAB developers to look into.

Style picker, song picker and multipicker all show up on the first monitor. But, I tried it again this morning (after waking the computer up from sleep) and everything is working fine. Very odd. So, to anyone else having this issue, try re-booting your computer (something I didn't try).