You know...that reminds me of an issue I haven't seen in a while, but a few of us have run into weird issues here and there where a plugin would stop working with CSI after like the xth track. So like, you'd have a plugin and it would work on track 1, but by the time you got to track 29 that same plugin wouldn't work. I always suspected that CSI just stopped working if you threw too many VST parameters at it. Like a dodgy plugin with too many parameters would blow up CSI so FX in the project after it wouldn't work.
Just a random thought. Might be totally off-base. Definitely talking out my ass. Never could figure out the exact scenario that led to this when I did see it, so just a guess.
Here's what you could try:
1. MPL has an import session data script here:
https://forum.cockos.com/showthread.php?t=233358
2. Install that, figure out how to use it
3. Try to recreate the problematic project by importing it into an empty project a few tracks at a time
4. After each new set of tracks, insert Neutron. Does it work? If yes, go to the next set of tracks. Does it stop working after a certain point? If yes, what was going on right before it stopped working? Was it a plugin with a ton of VST parameters? Can you recreate the issue in other projects? Anything else sticking out?
Alternatively, you could try this...
1. Take that same project that's acting up and move the track with Neutron to Track #1 in Reaper
2. Save As - give it a new name
3. Close the project
4. Reopen the project
5. Open the Neutron instance in track 1. Does it work now? If yes, what other plugins are in the project?
Let OCD guide you. There's a mystery afoot here.