I bought Vegas movie studio 15 steam edition. Having trouble exporting my movies

Normally selects MAGIX AVC / ACC MP4 When I need to make 1080P 59.94 or 29.97 FPS clips.

That's why I choose (Nvidia Nvenc) or without Nvidia But Typical mp4 format, also the videos I post, is also mp4

Small films of 30-50 sec, it can run smoothly, without any problems. But slightly longer movies of 3-5 min or longer. Then it returns maybe 10-40% and freezes. It just goes on, but can see in Preview that the video does not render anymore. Will have to shut down Ctl, everything and delete, and then say that program does not respond?

also rudder it has become slower to run. It takes forever to run a movie in 50 sec, (think it takes 7-8 min) and I have a powerful PC with 32 GB ram, 1080 cards, and I7 processor, so that shouldn't be the problem, as I said, it also has run faster when rendered with mp4, in the past

The strange thing is that I like to take a MainConcept MPEG-2, and then choose a m2t file that I have never heard of. Then it can run well, a video of 3-5 min or more without any problems. Plus it's also is faster

Then, for a while, I had to run an M2f file first, and then put it into VEGAS, and then run it to an mp4 1080P, but you can clearly see that the file was in through VEGAS, once before ---- so of course I want it to work.

Have tried uninstalling VEGAS, and afterwards confirm the files integrity under steam, unsuccessfully.

Can it be my Codec on my PC ?? it has worked before ... Maybe, where can you download the new ones that know it is the right file ??? Are there any other movie formats which are better ?? If you want to run 1080P. Or have some other good ideas, I will be super happy ... and will save myself a lot of extra work

thank you