At a later point in to the game (two floors down, to say as much without spoiling) the game seems to lock up for me in that when I try to talk to an NPC that doesn't move (sitting down or behind something) the game hangs up as if it's waiting for them to finish what they're doing except they never do and thus the game has to be loaded or restarted.
I've tried saving, restoring, restarting the game and talking to more than just the one NPC but this seems to persist.

reinstall?

Just tried that, it still jams after loading and trying to talk to an unmovable NPC. I can fish up the save file if it's particular to the save, since this issue has only started at random after going through half the story.

Seems to be something with the GOG version. I was able to play the game fully through on a fresh ScummVM, BASS, and the patched SKY file from the ScummVM website.

Are you Alt-Tabbing at any point in this game?? I have noticed that if you alt+tab out of the game you get stuck in one spot.

If it's the NPC I'm thinking of, then I had the same problem. Could it be...
*possible spoiler*
the bartender in the club? After I talked to him once or twice he started locking up for me too. He doesn't seem to play any vital role, however, and the game is able to be completed even after he starts freezing.

As I haven't gotten up to that part of the game on the GOG version, can't say if it's a game issue or not and it's been YEARS since I've played this. On the chance that it maybe, have you tried replacing the SKY.CPT file from the GOG download with the SKY.CPT file at the ScummVM site?

I played the game from start to finish running the GOG version without any additional patching required. I didn't get any lockups.
I would say maybe your save game is corrupt, but if you have restarted from the beginning of the game then it rules that idea out.
Have you tried re-downloading the game and re-installing it, then starting from the beginning again?

You sure it's actually stuck? Occasionally when you try talking to NPCs it forces you to wait through some animation of their's that is playing before anything happens.

Just the other day, I completed the GoG version of the game.
Only once, I had the game lock up completely. I did something to make Lamb go back into the factory, and he booted me out. After that, I couldn't move.
A couple of times, I tried to talk to a NPC who was going through a particular set of animations. After clicking on the NPC, the game would freeze up for a bit. Either, the NPC and the main would go to their talking positions, or I would have to click on the NPC again to get his / her attention.

Total thread ressurection here. But every answer so far has been silly.
This is just a bug with the Virtual Theatre engine - if the character needs to move to you and something is in the way, then you need to wait for them.
If you want this fixed - you'll need to pressure Tony Warriner or the ScummVM team for the source code, because none of them are gonna do it for you.

Thanks for the technical info. I just noticed it happened to me a few times. Before playing this game, I had never used ScummVM.

Well, I'm not sure talking to the developers would do much because when I used the ScummVM and SKY files from the official scumm website the game worked flawlessly start to finish. I'm not certain if this problem still persists, I haven't tried the GOG version again lately.
** spoiler **
It was talking to the kid on ground level, Foster would impotently stand in his speaking position next to the bench and the child would continously fiddle with his gameboy indefinately.