Bug - Media Encoder not rendering track matte's from After Effects... Still.
Media encoder is still ignoring track mattes setup in AE. When rendering, rendering said file with a track matte results in a cropped square instead of the required shape (in this case a circle). I've been seeing discussions of this issue since 2014. Doubling up on renders just to get around this bug is an appalling workflow bug. Rendering to Media Encoder continues to be unreliable.
Antoine Autokroma commented
What codec are you using for alpha channel export ?