In this post, the OP was having difficulty getting still photos to appear correctly in a 1920 x 1080 project.
Pan/Crop was ineffective.
He had prepared his media in a photo editor to match the dimensions of the project. 1920x1080 for 16:9 stills and 1440 x 1080 for 4:3 stills. The 1440 x 1080 stills appear to me to have triggered a pixel aspect ratio decision in Vegas that caused the media to be stretched until the properties of the media were changed manually.
To verify my conclusion, I prepared 4:3 media as follows:
One .jpg was cropped, but not resized, yielding dimensions 4864 x 3648. The same .jpg was also resized to 1440 x 1080. Here is a demonstration of Vegas 17 and 18 interpretation of the media.