When modify internal sync, the timeline changes

I’m on Debian 11 with Ardour 6.9. Now, I’m using Jack with Ardour and some external app (Hydrogen, etc). When I active the Jack sync all works fine, but I’ve noted that when return to Internal sync the timeline changes, specifically the frame info. The variation is minimal but it is. Why Ardour have this behavior?

ref

I found a video when we can see how the user change between Int > JACK > Int and the playback mark and the timeline don’t change. Please look from minute 5:24.

I think is a problem with the Internal Ardour process (latency?), 'coz I advice that info about latency is different between Qjackctl and Ardour (A post about that here). Well, I’m speculating.

I noticed something like this last night. I was writing drum patterns in Hydrogen while synced to Ardour through JACK. I noticed that the timing was slightly off. I wondered if I had somehow set the start of the project slightly late? I was able to finish the pattern and I exported the audio files expecting to have to shift them slightly in Ardour, but when I imported them, they were already lined up.

Initially I also ran Hydrogen + Ardour via Jack, never got happy, especially with tempo changes. Ended up with drum programming inside Ardour. The LSP sampler can load Hydrogen drum kits.
For a quick start the AVL drum plugins are a good choice (black pearl, red zeppelin), Both come in stereo and in multi-output versions, so post-procssing of kick and snare etc is easier
While MIDI implementation of Ardour is not best-in-class it is good enough to get the job done. Won’t go back.