--single-process is not an officially supported option, even Google only use it for testing purposes in Chrome. What are you using it for?
In order to get Steam features like Big Picture to work, without it users reported strange behaviors and even crashes.
The new 0.18.1 version was supposed to fix the use of the arg, I guess it's still broken.
Before creating a bug report on their git, I'd like to make sure that it's not just an issue on my end.