The dark screen of lag.. Oh, that is annoying..

It sounds as if your computer is having difficulty loading the encounter. Does your screen stay dark for a long time-frame, or does it eventually load ?

Best way to fix that particular issue is to save at that point, exit & reload. Take it as a subtle hint from the game that it might be time for a break. :) 9 times out of 10, it helps to just exit the game, & do a complete reload of the save point.

A tell-tale sign is you will see your party & toon will lag quite noticeably. If you notice this before a scripted multiple choice conversation situation - this is a particularly good time to save.

For new players, this can be hard to time, of course.. I suggest to follow the in-game advice & just maintain a good habit of saving regularly.

Mod combinations can exasperate the loading process ( KOTOR 2 being an older game; just be aware. )

One quirk that I've noticed with the game ( I've played since it has been released, on & off over the years via it's retail & Steam versions ) that it is processor heavy - even for a good PC rig.

The deleted content mod, for example, had been a particular swing & miss problem until a multitude of bugs were ironed out. More often than none, it is due to a mix of mods that are not tested & known to work in conjunction. The resulting conflicting programming is sorting itself out. Starting a save-game just after adding particular new mods ( versus a new game ) can also cause a crash.

Here's hoping all of this helps.