The problem for me seems to be opening a Reaper project which was using an older version of Helix Native (at least a year old I think). If I create a fresh project and insert a new Helix Native plugin instance it seems fine. It will load the project and close reaper a couple seconds after; Reaper at least recognizes the project failed to load and gives a notification on the next startup to not open that project.
 
	 
 
	I currently have Reaper v6.69 and Helix Native 3.50 installed.