In VP 19, media rendered with Voukoder x.264 is now flagged with a warning that it is not an efficient format for editing. I contacted Vegas staff about why this is happening and they reviewed the output and determined it was the very long GOPs. This warning was intended for highly compressed Zoom files.
For editing they recommended GOP length no greater than 1-2 seconds of footage (so GOP of say 30) whereas general purpose recommended, maximum useful cost possible, etc. are setting it to maximum lengths of 300, 480, etc.
I suggest reducing the GOP length of presets for x264 renders to facilitate further editing as some of us are using the output again in future projects.
Also, CRF for the general purpose recommended is also maybe higher than necessary? Default is 23 but it's at 17 which might better suit a high-quality preset.