Is there a bug with the magnetic mask in FCP11.2?

I just tried Magnetic Mask on 8 different ProRes RAW clips from 8 different cameras on FCP 11.2 and Tahoe 26.0.1 on an M1 Ultra, and I don't see the problem. If you can see it on various other clips on your machine, that would imply it's not the clip.

Please provide specifics about your machine and configuration: year, model, RAM. Also have you updated to Apple Pro Video Formats 3.0? That is part of the Tahoe update but you have to go back to System Settings>General>Software Update, and wait a few seconds for the update to show up.

You can verify the version of Pro Video Formats you're running by holding down the OPT key and selecting Apple Menu>System Information>Software>Installations, then scrolling down to Pro Video Formats and inspecting the version number. It should be 3.0.

I just tested the footage, works fine for me. If it's consistent, two things: Fill out the FCP feedback page (yes, the development team actively reads those and keeps them on file). Then call Apple support, see if they have a fix. If not, at least you've made them aware of an actual bug.

PS. I have mentioned the issue on a couple of FCP Usergroups on Facebook and have had several responses from other people who are experiencing the same thing. The main factor seems to be upgrading to Tahoe that has broken it.

I downloaded the sample file that you posted, applied the LUT and a magnetic mask. I do NOT see a line similar to what you are seeing.

Running macOS 26 and FCP 11.2.

I have the same issue. Material recorded in Prores RAW with a DJI Ronin 4D 8K and H265 with a DJI Mini 5 Pro Drone. So I dont think it's anything to do with the footage. I'm also running Tahoe and FCP 11.2.

[Edited by Moderator]

No, we'd need an original unaltered camera clip so we can investigate. If the current ones are too large to upload, shoot a 3-second clip, verify the problem can be reproduced, then upload that 3-sec clip from the camera.

I’ll sent a clip in the morning if I must but to be clear it doesn’t matter what camera or format the original media is in. I’ve tried it with ProRes RAW, H265s, H264s from a variety of different cameras in different resolutions and the issue is there with all of them.

So I’m not sure what use it would be for me to send you an unedited clip? Would be the same with literally any video file as far as I can tell.

others reporting same issue here. https://www.facebook.com/share/p/17UrNobEwt/?mibextid=wwXIfr

Thanks for the info. If you create a new test library, import a single clip, put that one clip on a timeline and apply only the Magnetic Mask effect, then analyze, does it happen then? Does the clip have to be a certain length? In addition to analyzing, does it have to be rendered to cache?

Do you see the lines when you export the project timeline to an H.264 file?

Yes, it happens to me too with a standard H265 file, AVC Coding, MPEG-4 AAC. But it also started to happen in 11.1 right after I installed Tahoe. So it must be OS related. The lines appear every few frames and it is a really painstaking problem to fix frame by frame.

OK I can reproduce it and will file a bug with Apple using the MacOS Feedback Assistant app. Will report more details later.

It is very rare I use the magnetic mask. I've always found it lacking in accuracy and consistency. I had need of it yesterday, and I saw lines on certain frames, just like the OP states. So yeah, bug for sure.

Indeed. I’m working on a project that was done in FCP 11.1 and Sequoia. I upgraded to Tahoe and the issue started happening. I expected 11.2 to fix it, but it didn’t.