When you merge two versions, especially with big apps and with larger differences between the versions, the editor will be noticeably slower for a little while after the merge as Bubble does a lot of calculations behind-the-scenes. This should resolve itself after a little while.

For more context, a large driver of slowness, is the actual pre-computation of conflicts from the way they are stored on the app after a merge to displaying them properly. We usually load large apps like yours in chunks, meaning we only load a given page when it's needed. However, right after a merge, we need to load "most of" if not the entire app, because there may be conflicts across many bits of the app, and we need to be able to visualize those conflicts (typically with a human-readable caption), which takes a very long time to load.