I attempted to switch from Authentic to the Church Builder Theme. (I also tried the Pneuma theme). When I activated both of the new themes, both the backend and the frontend of the site became very sluggish and at times unresponsive. It was bad enough that I reactivated Authentic. Any idea what would cause this?
That is frustrating. It sounds like it may be that the web host hasn’t allocated enough resources (like memory) to your site for it to be able to run the newer software smoothly. Typically when installing new plugins or themes, or updating the WordPress core and things are suddenly sluggish, that’s the culprit.
You might ask your host if they can allocate more memory to your site. If that’s the sticking point, it could make a big impact.