I have been having the exact same issue! I bought a lot for my legacy sims to stay in once they’ve passed away, because you can pass between home and the lot with the personal inventory - I had heard the ‘move graves’ option causes small bugs so I went with this option.
now my 4 generations are so laggy the lot is unplayable, but different community lots, different households, no problems - as long as they don’t own businesses!!
really upset by this being a damaging bug, I’m also having the car glitch where their car lags and resets every-time you use it, and the vacation bugs - I can’t go anywhere on vacation at all. All of my favourite things of the gameplay are unusable :(