When holding a map in the offhand slot, the crosshair vanishes. The brackets for Reacharound Placement also do not appear, though placing blocks still works as intended. Removing the map causes both to reappear.

Both client and server are running pack version 1.1.2 as provided on CurseForge.

Upon further inspection, I realized that the crosshair only disappears when holding a map in the offhand slot. So it appears not to be a multiplayer-specific issue like I initially thought.