I just switched in General from "use system language" to English US... My local language GUI was really annoying in both Configurator and Master, and in older versions there was no English option for some reason.
In 4.1.0 I just noticed there is English. The moment I switched to English and reopened Configurator, clicking "Start service" worked right away 😮
The line
[WARN] WindowsServiceControl: 'VeyonService' could not be started.
is not showing anymore in .log
So far no errors, everything looks fine. Going to install it on few class PCs and see if Master works without issues.