Freeze on Startup Workaround
Repetier-Host freezes on starting the application, seemingly randomly. The splash screen shows, most of the application appears to load, except the 3D View, and the splash screen never goes away. I am currently running version 2.1.6.
TLDR: If using multiple monitors, try deleting registry entry "HKCU/Software/repetier/window/mainWindow", and don't close the application while on any other monitor than the one it originally started up on.
After battling this issue for months now, always resorting to deleting the Repetier registry entries and restarting the application, I am confident I finally found what is causing it to freeze on startup. I have 3 monitors, and moving the window over to another monitor, closing the application, then reopening it will result in it freezing. I discovered that deleting just the registry setting "HKCU/Software/repetier/window/mainWindow" or setting it's value value to "234|234|1034|569|Maximized" fixes it and I can continue using it as before. The value is saved back to the registry the next time the application is closed. This also saves you from losing any printer or slicer settings by deleting the entire Repetier section in the registry.
If it helps to track this bug down, the value when it fails to start is "-1480|335|1034|569|Maximized".
Hope this helps anyone with the same issue I have, and sorry if this workaround has already been posted, but the only search results I could find were the original workaround I mentioned above (and just now after a quick double check, also deleting the "window" section of the registry, but at least this narrows it down to a specific value).