I am not exactly sure for the solution for this. But it happens because of caching issue mostly on the browser side.
Also it can happen if your instance is running on multiple nodes and the theme is not applied on all the nodes.
Clearing browser cache and restarting the browser generally solves the issue.
Hope this will help in understanding the problem.
I don't think that this is the issue. When I tell Jive to change the global theme (and use the same one again), it works on the first load of a front end page. The Issue also appears when no changes are made in the theme and the displayed page doesn't just show a cached version of the styles, but rather a really messed up view of the OOTB theme. Our styles and scripts surely aren't cached in the browser, because they are assigned an automatically incremented build number everytime.