In realms servers (and possibly also classic servers, I haven't checked that) chunks now unload on the client-side when moving beyond the server-side render distance, meaning even when the client-side render distance is set to 64 chunks, it's actually capped to the server-side render distance (which I believe is 10 in realms). This constant unloading and reloading is causing many lag spikes as I move around my base instead of just one on the initial load, not to mention that now I can't see nearly as far as I used to.

In the attached clip you can see that despite my render distance being set to 64 chunks, everything unloads as I fly away.