Draw Mask visible in transitions

I have a draw mask and a yellow background. And all works fine but as soon as the transition begins the draw mask turns from yellow to black. Any idea how to solve this problem?

Yeah, FCP has an issue with transitions interfering with stuff. You'd think they'd work that out after 10 years. Anyway, try placing that clip into a Compound first. Or try keyframing the Opacity manually. It always baffled me how keyframing opacity could work when the dissolve transition doesn't.

Compound clip didn‘t work… And even when I render the video and use the clip in an other project I have the same problem... 🤔

I'd need more details about what exactly it is you're doing.

First of all thank you for your help! 👏

I have an objekt in front of a white background. And I want to mask out the stand of the object. I have attached some pictures that are showing what I want to do. In the end I have two problems:

1) In the transition the mask is showing black and not the white background
2) On my computer it looks fine but when uploading the clip to YouTube I can see the mask grey (when taking a screenshot it is white so I had to take a picture with my phone from the screen 🤷‍♂️)