PNG clip won't show in front of other clips

This is bizarre. I have a new PNG clip I'm inserting into a video track. When there are no other tracks behind it, it shows just fine, but there is another video track behind it, it is invisible. Other PNG clips work like normal, even in the same video track. I created the PNG using Affinity Designer, which is what I created the other ones with. All the color and transparent settings are the same for all of the files in AD before I export it as a PNG file. The only difference, other than the contents of the graphic, is the size. The one in question is very long horizontally, because it's a timeline and I want to slowly scroll it across the screen. Seems very bizarre that this would causing the problem.

Within DR, the PNG clips have the same default settings, including 100% opacity. Any thoughts? This time line is quite crucial to my project.

DR has a limit of 16,384 pixels in both dimensions. Are you exceeding that?

I didn't realize that. The answer is yes, by 126 pixels, which were easy to remove. Now no problem. Thanks so much!