This is not an issue with slick theme, it was related to a bug in core https://github.com/NodeBB/NodeBB/issues/6306
dangerusslee created this issue in NodeBB/NodeBB
Some bootswatch skins broken
NodeBB address in use, exiting... Error: listen EADDRINUSE 0.0.0.0:4567
This usually means that NodeBB is already running. Use ./nodebb stop and if you still have the issue look up "kill process on port" with a search engine.