You put in lots of work into that project. It takes time to fully cache. Be patient. Proxy editing, a common practice, is worth a study...
See... https://nch.invisionzone.com/topic/26563-proxy-editing/
There's no need for 4K on files 1550 and 1556. Suggest that the finals of those be reduced to HD. My guess is that the 1550 is causing the most issues. When replaced with a downconverted HD mp4 things went much better.
There are some editing errors...
Flash frame/s at approximately 14:505
Black gap at 1:23.135
4:03.662, a very short clip, possible error
Gap at 4:19.811
Gap at 1:45.127 And a few others in the way effects were ordered.
If the reverse at about 16:00 freezes, pre-produce the reverse. Then drop in the new clip in normal mode. Add the efx.
Using Pan & Zoom and Zoom or duplicate effects within the same clip may cause problems. As an alternative of pan and zoom, try instead animating the Zoom effect. The fonts need to be smaller to fit the screen. Also, use as few tracks as possible. Some small clips can be placed on existing tracks where there's a gap.
VP is non-destructive: changes made in Videopad won't affect the original files.
Check your PM for the revised project that incorporates the above changes and the HD export. (The result may not precisely match your efx but you can tweak.)
Use the 64-bit version of the program... https://www.nchsoftware.com/download/videopadsetup64.exe
