When opening projects saved with Melodyne 5 ARA instances, REAPER frequently crashes. Generally the workaround is opening the project in Safe Mode and manually Onlining all plugins, but this is time consuming and annoying, and doesn't permanently fix the issue.
I previously owned Melodyne Studio 4, and experienced none of these issues until upgrading to Melodyne 5 last year
Running Reaper v6.23, on Mac OS X 10.14.6
Melodyne Studio 5.1.1.003
Crash report attached.