My understanding is that the SPP is updated periodically during playback, an alternative to MTC.
https://www.sweetwater.com/insync/song-position-pointer-spp-2/But that feels like overkill…
I think what you have done should work under most circumstances.
My aging brain is now recalling similar issues with SONAR in the past from the SONAR forums - not rapidly responding to transport changes. SONAR is for production, and will attempt to reconstruct the audio sample-perfect every time at every point in time. So… If you set the transport to point A, it may need to reconstruct point A by looking at all points in all tracks prior to point A, as there might be effects trails, or long-held notes, etc., that should still be in effect. It doesn't just go there & play. So while it follows transport, you might get a pause at start. I think the stop/start to do a loop basically kills the audio engine, as it can't do all that work instantly. That's my theory anyway… I am still experimenting with Matrix View (their real-time looper…), holding out some hope, but no joy yet. Looping is very flexible, but I think it wants to be the clock master. It would be
perfect if you could slave Matrix View to Jammr…
I should note - I've been using SONAR quite effectively with Jammr, with no noticeable drift - I recently shared a recording of it. I just have to manually sync the tempo & also to the metronome. I want it to slave outright. And to queue up requested changes to the start of the next interval (a Matrix View function).
Moebius scared me… It is quite old, and my first attempt to fire it up on Win10 caused a BSOD. I haven't seen a BSOD in a long time. I immediately de-installed it.
Hollyhock doesn't have an out-of-the-box sync, BUT, it has sufficient tools to build your own… And it hosts VSTs. I will experiment there at some point.