That is super weird. The only thing I can think of and have experienced is that you’re working on a mp4. I’ve experienced issues before when trying to do something quick on an mp4, as soon as i swapped it out for an mov the issues went away. So maybe try converting to an mov or mxf and see what happens?
Ascenders/decenders never play well with anchor expressions. The solve is to use the x-height rather than using the bounding box. I always use the following as reference on how to do this. They utilize some presaved effects in their documentation, but if you understand expressions it is relatively easy to understand how to apply this to your project. I hope this helps.
What are the pixel dimensions of the artboard? Also is the file in RGB color space? First things that popped into my head that could cause issues potentially.
It’s seeing it as an audio only layer. Maybe try right clicking on the file in your project panel and selecting interpret, see if the video portion is turned on. Otherwise if it plays fine from file explorer maybe re-import it to the project. Something is causing AE from recognizing the video track.
You can use “b” and “n” to set the beginning and end of your work area. Set your preview settings to only render the work area. Then it shouldn’t shift.