The "mp4box --add" was all i wanted you to test, this way you changed the mp4 container from ffmpeg to the default one from mp4box. Currently we have no indication that any special "box" in the mp4 is missing, i just wanted a different container manufacturer but the same essence.
After testing the CBR setting, did you see the "Overall bit rate mode=Variable" gone in the new file?
To give you some insight, what i do for this kind of incompatibility issues, i first need to get out if it is about the container or the video/audio stream.
To be honest, i am still not 100% convinced that the container is out of scope here, but still, my next steps would be:
-) check for logs from protools that may indicate if the problem is in container or video or audio (or metadata)
Instead of the Delivery node. After Encoding, the File is located in the cache directory of ffastrans. When you rewrap you can just specify the final destination path as output path.
BUT you should not automate anything in ffastrans (or anywhere else) until you exactly know what to do, so first get out whats causing the incompatibility, then automate the solution
Next steps for me would be to try to remove the video from the non-working mp4 file by using "ffmpeg -codec copy -vn".
If that works, we are pretty sure that it is about the video encoding properties and need to try to recreate all possible stuff from the working file into the non working file (my first guess would be b-frame related stuff)
-- done for today --