Originally I only had the 64bit version of the plugin installed, so I couldn't run the project in FL 32bit.
But now that I've installed the 32bit version of the plugin, both instances open happily in FL 32bit. ...
I just installed FL FLowstone (formerly FL SynthMaker) and loading the Synthmaker plugin does this:
[img:2zrpityk]https://i.imgur.com/XtlG1bF.png[/img:2zrpityk] ...