Use the profiler to know why game is lagging

Hello !
I have a problem in my game… I have a lot of lags. But that is strange, because it is really recent.
I mean, I did several cities in my game (map with world composition). And I hadn’t any lags before but since I ended my last city, I have a lot of lags even in my first one…

The lags happen when moving in the world with editor or with player in some specific place of the city. Deleting a light in this area and then do a CTRL+Z to cancel the delete often unlock the situation for a while.

So, to understand the problem I tried to use the profiler. So I followed several tutorials but never find what exactly was the problem;

I discovered that it was caused both by the game thread (62ms average, 455ms max) and the render thread.

When I look at was is causing issue in game thread, it is written that is the “Frame time” (62ms) and in this the “frame sync time” (28ms). The “world tick time” is at 8.9ms so, it seems to be high… But when I think about it, that isn’t the only problem since it is only 8.9ms of 62ms… I will look at what is causing it but I have no idea how to reduce the “Frame sync time”…

Here are some pictures :




About the render thread, the problem seems to be due to a lot of things… Including shadows projection, but I have no idea how to reduce them…

Would someone help me to understand better what the profiler is saying ?

I am using UE 4.26.

Thank you for your help and your time !
All the best