At least in the past, SmartScreen did “warn” me for some dev versions of RT installers, and after clicking “Allow”, the installation was still broken. PTGui is a commercial program, and even with 2.0k of clicks on the link for development build of RT for Windows, this is almost nothing, RawTherapee is an exotic outsider, suspicious, when checked against MS database. This might become worse in the future.
Even if nothing crashes, running dbg with the debug version (perhaps also setting verbose to true in options, I’m not sure about this) may show something.
The program start seems to be still slower than gtk2 version was, but on your computer, it should take about 5 seconds, at most.