@nonboingy What setting are you using for High-detail Lots, and does it help to change the setting? This is the number of lots that are fully rendered by the game at any given moment. Please also try flipping the Enable Object Hiding setting from whatever you're using now. Make the change at the Main Menu and quit to desktop before loading a save.
Do you own University Life or Into the Future, and if so, does this happen in other foreign worlds too? If you don't own one of these expansions, you could use NRaas Traveler to travel to a different EA-made world, which would be an interesting test.
Also, try setting your laptop to only use the AMD card, at least while you're playing. Open System Preferences > Battery > Power Adapter, and uncheck the box for automatic graphics switching. I believe there are two separate settings under Battery and Power Adapter, one for each mode, but check the Battery subcategory if you don't see anything under Power Adapter. The point here is to prevent the system from trying to switch back and forth. And play with the laptop plugged in at all times.
It's interesting that HomeOpener gets around the issue since its presence means that all the houses are open all the time. But then, so are community lots, and you already knew those were unaffected. HomeOpener does increases the game's resource use, at times by a substantial margin, so it would definitely be better to find a fix.
As a side note, in case you weren't already aware, you'd need to manually "close" the houses with MasterController after removing HomeOpener from your save, in case you want to test in your current save and don't have a backup. On the flip side, it makes me wonder whether "opening" the house manually before your sim shows up would work too. It's an option in the MC menu you see when clicking on the house itself, its map tag, or the ground.
