Love Struck world lots not visible in older save files (works in new saves)

Recently bought The Sims 4 Love Struck expansion pack. The new world loads correctly in saves created after installing the pack, but in my long-term/older save file the world appears with no visible lots on the map and grey boxes over the apartment blocks.

I can select locations in the Love Struck world for planned dates and events, but I cannot access the world from the map view, move Sims there, or see any lots.

I play on PC. I do not use mods or custom content and never have. I deleted localthumbcache.package and repaired the game. Issue persists only in older saves but works in new saves.

This appears to be a save compatibility issue rather than an installation problem.