Editor freezes often after project version switch


We have recently converted a 4.15 project to 4.19.2 and since we did that we have experienced some freezes in the engine. Like, we select some assets or move or anything really and the engine will stop responding for a few seconds or even sometimes like 2 minutes.

It seems the problem happens more often on larger map.

Does anyone have any idea of what it could be ? Or could you tell me how I would go about debugging this as it is not crashing ?

Thanks in advance =)