I’m using Libre Office on a Dell laptop. Resources are fine, Intel i5 and 8 gigs of memory. I started experiencing this after upgrading from 4.0.2.x to 188.8.131.52.
What happens is that I have to wait for ~ 3 seconds after double clicking a cell or pressing F2 until edit mode is activated. The same happens when I exit edit mode. Worth mentioning that this is happening only after I do some work in the file, maybe 10 minutes or so. If I close and reopen the slow edit disappears to reappear in a few minutes.
I didn’t yet notice whether the time lap between triggering edit mode and actually entering edit mode increases with time.