Show Layer Glitch

This is the second course I've made where I have a glitch when showing the first layer of a slide. On the base layer and all layers after, there is a header that is copy pasted throughout the course. They are all positioned at the very beginning of each layer's timeline and show to the end, so it only looks like the content underneath it changes. However, a have a layer where that header glitches when it first appears. There are no transitions on the page or animations on any header objects (a shape, text box and a logo). The header is placed at the top of the timeline, so nothing should interfere with being in front of it. I cannot find anything different about the header on this one slide compared to the others. All objects are all in "normal state" with no other states created. If anyone else is having this problem or knows what more I should look for, please let me know. Everything else is smooth except this ONE layer glitching at the very beginning. It appears like a flash. The trigger to move to that slide is "when the timeline ends, show layer__________", like most of the others. The glitching header slide has a video that plays underneath it. That video is not overlapping the header on the screen.