The Vero 4k has be excellent in playing whatever I’ve thrown at it but curiously I found a random MP4 file which it only plays the video part, no audio. The file plays fine in Linux Mint using both SMPlayer and VLC. Also plays fine on a LibreElec generic x86 system.
I understand you might not want to disclose the source, but if it was an upload, the person who released such a video should be chastised with a rough brush.
If you find any other problematic clips, let me know and we can look in to it.
AC3 upmixing can work around some interesting encodes, but they are very far and few between.