I have a ridiculously powerful system and when Vegas freezes at random, I don't see anything in the Performance Monitor ramping up, so this isn't a disk or memory bottleneck, GPU / CPU overload, etc. This can happen with a 4K video project or a 720p project with minimal edits. For every bit of work I do, a specific Project is created to handle all the assets.
Intel Core i7 9650X Xtreme Edition processor
G.Skill Trident OCZ RAM, 128GB (@8 x 16), XMP enabled
2 x nVidia GeForce RTX Ti Founders' Edition video cards
Windows 10 64-bit running on Samsung 950 PRO series M.2 SSD
Working on a RAID 0 array of Samsung 850 EVO series SSDs (2 x 1TB)