This is the bug reports forum for Leadwerks Game Engine, but I will answer your question here.
Currently, the new version 1.4 beta is on the default branch on Steam. You can opt into the archived version 1.3.11 by right-clicking on the app in the Steam interface, selecting the Properties menu, and then select the Betas tab on the left.
Version 1.3.11 seems to be the most stable, and it seems that perhaps later updates in the source code repo might have introduced some graphical problems. I located the point in the code history that corresponds with 1.3.11 and will use that as my starting point from here on out.