FCP 12.3 timeline issue loosing audio feedback on the timeline.

I have found a workaround at least for me. The issue happens for me when I use the shortcut B for the blade and make the actual cut with my L mouse button. Sometimes it takes about 3 cuts for the sound to cut off and the video to no longer skim.

Using command+B to make my cuts directly in the timeline without toggling the blade doesn’t cause the issue. It is also faster to edit now 😆.

Reinstalling won't help with this.

Verify your system drive has at least 15% or more free space.

If editing on an external drive, make sure it's not filled up, and is formatted APFS.

Delete all render files.

What format are the clips you're editing?

Try deleting FCP Preferences/Settings. Hold option and command while launching FCP and choose Delete. Set FCP preferences/settings back to the way you like and see if the issue has been fixed.

The only potential thing I see is autoupdaters. In the past, Google's keystone autoupdater software was notorious for breaking FCP often requiring a complete uninstall of Chrome and an uninstall and reinstall of FCP. I'm not sure if Google's new updater is still problematic. I do see that MS's Edge autoupdater appears to be identical and the advice here has been to remove Chrome and use something like Edge instead. Hopefully others will chime in on this.

[Loaded] com.google.GoogleUpdater.wake.plist (Google LLC - installed 2026-07-02) Command: ~/Library/Application Support/Google/GoogleUpdater/Current/GoogleUpdater.app/Contents/MacOS/GoogleUpdater --wake-all --enable-logging --vmodule=*/components/update_client/*=2,*/chrome/enterprise_companion/*=2,*/chrome/updater/*=2 [Loaded] com.microsoft.EdgeUpdater.wake.plist (Microsoft Corporation - installed 2026-06-26) Command: ~/Library/Application Support/Microsoft/EdgeUpdater/Current/EdgeUpdater.app/Contents/MacOS/EdgeUpdater --wake-all --enable-logging --vmodule=*/components/update_client/*=2,*/chrome/enterprise_companion/*=2,*/chrome/updater/*=2

Is your footage and/or FCP libraries stored on OneDrive or iCloud Drive (Desktop or Documents folder), not local?

@BenB - Apparently iCloud Drive temporarily locks files in the sync'd folders when syncing with iCloud. I think the bigger issue is trying to edit with files you think are local but could actually be coming from iCloud. Quite a few users here have been caught out by this over the years, so it's good that FCP now prevents it.

Where are these .m4a files coming from?

Do they open in QuickTime Player and playback correctly?

Try taking them in to Compressor and converting them to AIFF or WAV files.

How are you monitoring the audio? Through any kind of external interface?

Please post a report from https://etrecheck.com using the "Additional text" button below in your reply. This anonymized report can help us to identify if there are any system related issues.

Okay, good to rule iCloud Drive out for your storage locations. I don' think having the FCP App itself sync'd is a problem.

So according to your etrecheck report it seems at one point you had Chrome installed so possibly there's some leftover cruft. Follow the instructions at https://chromeisbad.com to completely remove any and all remnants of Chrome. It's not enough to just delete the app, there's a bunch of other software they install that needs to be removed.

Are you by any chance saving or accessing media to a location that is syncing to onedrive, or icloud?

Did you migrate from another machine? Did you install any "cleaner" software? An etrecheck report would help us to identify potential problems.

Is there an issue with FCP editing MXF files now? After updating to 12.3 I am also unable to playback clips in the timeline, especially with audio fx applied. It drops frames after 2 seconds and I loose all audio. The only solution is to have FCP 'render' the audio effects, which takes a really long time.

Get rid of Google! ALL OF IT. You don’t need it and it is notorious for causing problem with Final Cut. Use Firefox or Safari for your web browser, not Google Chrome.

I’ll bet that once you get rid of all the Google stuff, things will work OK again.

One more thing…the word is “lose” not “loose.”

@O_V_G, OP @AlertSense said earlier, "I have three browsers. Brave, Edge, and Safari." so doesn't look like he's actively using Chrome. He may have deleted Chrome.app but not all the other cruft that is installed, which is why I recommended following the instructions at https://chromeisbad.com on how to completely remove it.

What percentage of your hard drive is still free space?