Slow performance on long timelines

I am wondering if it is an usual phanomen. When i am editing a longer project - let's say 20 - 30 minutes - and I want to see the full timeline, or at least a longer part of it, my playback rate drops down to 10 - 20 fps. When I zoom in, it plays back smoothly.

It doen'st really make a difference, if waveform are switched on or off or other settings for the clip preview. Right now I am working on a 1080p25 project in Prores 422, original files stored on a NAS, Cache on a USB3 SSD, database on local SSD.

[Peter Chamberlain]

What is the playback rate on the color page?

Quite constant 25fps. (With no grading)

Maybe not the issue, but what thumbnail mode are you using in your timeline? I've found with heavier timelines that having thumbnails set to filmstrip (as opposed to head / tail or off) can incur a huge penalty.

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I am seeing the same problem.
Zoom in the timeline for better playback.
Zoom out and it gets quite slow to get to speed.
Still gets to 25fps but takes about three times longer.