Lag in Inspector on Compound Clips?

I sometimes get extreme lag when adjusting parameters in the Inspector, such as the Color Board. Prefs deleted, nothing else running (except for Screenflow to capture the video below), Computer freshly rebooted, Final Cut Pro freshly restarted. Makes no difference.

Here's the scenario to see if this effects others: 4K clip in a 1080p timeline. Clip has gaps removed so only the relevant parts are on the timeline. Clip(s) are then Compound-clipped into one as I do a gentle push with the incredibly exciting Ken Burns™ feature. Color adjustments are done on the Compound Clip and this is where it is laggy. If I go inside and do the color adjustments on the OG clips, it's fine, but then of course I have to copy paste the grade to each clip.

Watch or Download this video of the lagginess:
www.gamesack.net/crap/Lag.mp4

What the Screenflow-made video does not show you is the times the cursor turns into a spinning beach ball. Not sure why Screenflow omits that.

Using:
MacOS 12.5
Final Cut Pro 10.5.3
Mac Studio M1 Ultra (I suspect this may be the cause of the lagginess unless others on different machines can reproduce this)

EDIT: I cannot replicate this in a new Library. I'm guessing FCP has a limit on what it can do as far as complexity? It only wants to do simple things less than 30 minutes? What causes a growing Library to lag? My current Library size is only 480GB, so pretty small still.  I've worked with bigger Libraries in past versions of FCP on older computers that did not due this.

Redifer thanks for reporting this. I am looking at it. Inside the library there is a separate SQLite database for each event and one for each project, duplicate and snapshot. Normally performance is good. There is generally not a hard limit on library size or event size.

However there can be a performance issue on a long timeline (IOW over 2 hr), if it is also very complex with thousands of edits and effects. In that case the SQL database for the project can potentially be over 200k rows. If you were to hypothetically export that as a .csv file, even a lightweight tool like QuickLook would take a while to open it -- just for reading.

The main table (called "Collection") is not read only but must be updated each time you manipulate the timeline, adjust the controls of an effect or apparently just draw a selection box around some clips. That SQL table has multiple indexes so each update must also update the indexes.

Ideally the UI update should always be on a separate thread which should not block on a long-running operation. The normal practice is the developer would show a wait indicator (progress bar, etc) on the UI thread while a secondary thread runs the task. That way the UI remains responsive. However if the software code path for a given user action and database configuration becomes very convoluted or reentrant, and if the FCP developer did not envision that scenario, in theory the UI could become quite laggy and sluggish. That seems to happen in some edge cases. There could also be possible involvement by 3rd-party effects (not necessarily your case, just in general). 

Could you send me a ZIP'd version of your library, with no cache, data or analysis files? I also need to know the event name and project name. I could study that for some clues, also test it on my machines and examine the I/O profile for the database. I don't need your data for that, just the library.