I created issue yesterday, which was ranked "Duplicate" (MC-74881) So I read this issue. I sought the cause of lags. I broke all the stained glass of my city and I replaced by normal glass, and lags have disappeared in this area. I had 2 fountains, I removed the water, lags have disappeared too, and I still find a block that creates lag, but otherwise I have almost no lag in my city!

So I think there's a problem with transparent things.

Mr_coco29

PS: I'm French