lag bad since 1.2.3 and at night-fall becomes INSANELY bad

Since last 1.2.3 update (which coincided with a W10 creators update of Windows) I've had lag for 1st time in my world. pretty bad, running around half speed. i stopped all the fancy features in video settings, e.g. clouds, and it's a bit better but not like before.
[by the way, in my village there are a LOT of mobs: villagers, golems, livestock... but it never slowed down my movements before.]

then i noticed something that happens as soon as night falls. at that very instant the 'lag' becomes MUCH MUCH worse. just now, i clicked on my bed to sleep at the very instant night fell, and it took around 40 seconds to complete the sleep, whereas normally i guess it should take about 3-4 secs, right?

i have seen on the forum and elsewhere here that i'm not alone in experiencing this bug, particularly the night-time one.