Session Strings Pro (Native Instruments)
Track has "Session Strings Pro" loaded in the "Kontakt"-plugin from Native Instruments. Track is marked with ">C" (copy tracks to instrument-project or vice versa) and project processing is launched ("MC-PP").
Reaper crashes half way through the process.
Save the setup in Kontakt (multi), remove the "Session Strings Pro", launch "MC-PP", load the saved multi in the copied track. Or replace the sound with e.g. "String Ensemble" (if available).
This problem occurs with the version 11 of Komplete. Version 12 is out and will be tested in the near future.
Working with subprojects.
While it is possible to create backtracks from tracks holding subprojects, it is not possible to copy those tracks to or from instrument-projects (">C").
Create stems instead of subprojects or create stems from the subprojects.