There have been a couple of threads about problems with Mp4 files. My problem is with Handbrake created files which is of concern as Handbrake is frequently recommended as a Vegas friendly file convertor.
I occasionally use Handbrake to convert my 50i mts camera files to 50p Mp4. The Handbrake files work perfectly in VMS16 Platinum and I'm pretty certain they were working well in VMS17 Platinum until now. Maybe Build 204 is causing another problem. Both VMS16 and 17 are using, or trying to use, "so4compoundplug.dll". The problem is that VMS17 is reluctant to import them and doesn't play them well. So badly they usually freeze the video while the audio continues.
Here is a link to a short file I've uploaded to Google Drive
I'd be grateful if others could try it with VMS17 Platinum Build 204 to see if you have any problems, or whether it's just me. Thanks.