Thank you for reporting this issue. This appears to a problem with the .mp4 decoding. You might try disabling "Enabling hardware accelerated video decoding" under Preferences > Import > Video Footage.
Additionally, would you be able to share the glitching footage with us? If we are able to reproduce the issue, we can investigate a potential fix.
Thanks for reporting this issue and for any further information you can provide,
- John, After Effects Engineering Team