I use VEGAS Movie Studio 15.0 on a Windows 10 PC. I convert MOV files taken on my iPhone X into MP4. Lately, the resulting video appears shaky and fuzzy (the source files are not). The problem is both on PC and if I upload to Youtube and watch on TV so it's not the PC issue. Both the source and destination are 1920x1080. Previously, the same software converted my files with no issues.

Did anyone have the same issue and do you know what to do? Thank you.