Ok this is a lot more clear 
You have the option automatic offline turned on, and version 8.5.0a use a version of a library with a small issue, meaning that Yatse in some cases can generate quick false offline status. So Yatse automatically revert to local device player as it’s what the option does.
You can disable that option until next version is out.
Only thing strange is that changing the player in that case should stop Yatse on Chromecast, I’ll try to find why it did not happened.