Ardour slow with multiple playlists and takes

Hi there,

I recorded an orchestra last weekend: 30 mics, 11 stereo tracks, 8 mono tracks.
The mics were plugged in presonus digital stageboxes, sent digitally to a presonus Studiolive 32 mixing board, latest generation. I used the mixing board as a soundcard and a MacBook air to record the whole thing and send click tracks from ardour to the conductor.
Altogether the setup was a breeze and worked at the beginning as expected.
I usually use Linux and ardour for studio recordings, but due to the high channel count and the AVB setup of this concert hall, I had to use MacOS.

The orchestra played music for an audio book, so it’s a lot of small pieces (21), 30 seconds and up to 5 minutes long.
We decided to record in small chunks and had to do a lot of takes sometimes (ok, the orchestra wasn’t as good as expected). I decided to create a new playlist for every take. After 2 hours of recording, I had over 100 playlists. I read in the manual that playlists are cheap CPU wise so I opted for this option.
The problem was that scrolling back after having recorded a bit of music started to be extremely slow. I had to wait over a minute for the playhead to react again, I then moved it to the start of the take, then it switched back to where it was, then became reactive and I could move it around as I wanted to.
It’s an unpleasant experience to have an entire orchestra wait several minutes after a wrong 10 seconds take.
I had the feeling that it took a lot of time to draw the waveforms, and that’s why ardour wasn’t reacting. But it got steadily slower with more playlists.

I also experienced 2 sudden crashes during the recording. While it was not a big problem in this context, I felt quite a bit under pressure.
On the other hand, navigating the project after having waited is not a problem.

To summarize:
With a lot of playlists, the playhead freezes directly after having recorded something.

My questions:
How can I avoid this without changing my workflow? Where is the bottleneck? Is it graphics? RAM? CPU?

Feel free to ask for more detailed information