Large number of captions slows down the whole application (v22)
From initial testing, this is still present in the new 2022 version (though this is testing opening up 2021 projects - it might be different starting from scratch.)
If you have a large number of captions open in a timeline, say you might have a 1 hour interview in a foreign language with captions - it slows down the whole application, whether clicking around in the timeline or clicking on folders or clips in the Project window.
Workarounds
1) Hide the captions via the CC button in the timeline - this solves it & you can still edit the captions and they still show, but means you can't move them around or change their timings
2) Zoom right into the timeline
3) Nest the timeline - but with no good way of decomposing nested timelines, this can create a lot of work later
4) Sometimes copying and pasting a timeline into a new project will work too

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Manuel Razzari commented
Closing the "Essential graphics" panel while working on subtitles produces a major speed boost. Not 100% fixed, but improved.
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RJS460 commented
-Thank you for creating this!
- It would be great if it could get fixed.
- I created a keyboard shortcut to hide captions which has been helpful because it lags so bad when the CC are up on the sequence, it can take 2-3 mins just to click and turn them off