Does anybody know what to do about invisible sims? The other day my own sim was in the park and I noticed sounds of chess playing going on nearby. The figures on the table were shifting and I could hear voices. There was at least one sim sitting there but totally invisible. I couldn't mouse over him/her to find out who they were. I have Nraas debug enabler installed but that doesn't seem to do anything.

By itself, NRaas DebugEnabler doesn't do anything. You have to 'trigger' it to act.

Follow the steps here: https://nraas.wikispaces.com/Invisi...ms+-+Stuck+Sims

I triggered DebugEnabler and it recovered another sim and a lost raccoon (I really didn't miss the annoying little sod), but my invisible chess player(s) remained invisible. I've just installed the latest version of Overwatch for my patch level, I'll see if that fixes it.

go to edit town move him out and back in

Here's another trick if Fix Invisible Sims doesn't work (it sometimes doesn't work for me): if one of your Sims already knows the Sim who's now invisible, go to their relationship panel, click on their portrait -> Nraas -> Master Controller -> Outfit and select any outfit. Your Sim will most likely be visible again
For this, you will need Master Controller. You don't need any extra modules, just the base mod.

The trouble is, I can't find out who he/she is in order to follow these suggestions. My sim was in the park again just now playing her guitar for tips and at first I didn't think anybody was interested. Then I heard somebody cheering and somebody put money in the guitar case. Later another visible sim got into conversation with the invisible one and speech bubbles were appearing just above the ground just in front of her. That's why I couldn't click or mouse over them, they're underground! I tried pausing the game as suggested above, but to no avail.

Get Nraas Tagger. All the Sims in the neighborhood will now have tags visible from Map View and you'll be able to find out their names.
If you get Tagger and Master Controller, you can click on their Map View tags and change their outfits like that, without having to go to the relationship panel
You can remove Tagger afterwards if you don't want/need it.

The Sims themselves are NOT underground, they just don't show up at all because their outfits are borked. With fairies, only their wings show. With other Sims, only thought/speech bubbles will show, and the plumbob (if the Sim is part of the active family).

Actually, I just saw this in my game last night where I went over to annother teen's house and his mom was yelling at the air. I know insane Sims do whatnot like that but there was the symbol of double relationship loss and I used MC and she didn't have the insane trait. It reminded me of this thread. Also, sweetdevil, you reminded me of how I've had my Sim invite over one of her boy toys but he was invisible and sunk through the ground. The grass was getting weird thought bubbles, lol.

The problem was that before I moved him with "moveobjects on" and put him in my Sim's sex slave dungeon (in the basement) and didn't move him up to the ground before I reset him. It was amusing to see my Sim makeout with air before he sunk down into the black abyss where my Sim stamped her foot and complained that she couldn't woohoo with one of her nine official lovers.

So tragic.

When I do the cheat between floors as well I'll have my Sims walk up the stairs and then they'll just walk right through the floor once they get close to the top of the stairs. That's also funny.

Elynda, you could just "resetsim * " and reset every Sim if you don't mind your Sims being teleported home. I also like using MC's function of resetting the whole town. It cleans up some lag if I suddenly get some.

Annything: I tried your solution and it worked. The reason I knew was that, by a coincidence, one of the invisibles turned out to be a sim that my sim had to paint a picture for. When I invited her over to collect the picture, there she was completely visible and above ground. And sweetdevil, that's an excellent idea, I don't know why I never thought of it before. I've had Tagger installed before, but didn't see much use for it cluttering up map view, but installed temporarily it would be very useful tracking down problem sims. Thanks to everybody for your suggestions.

Glad to know you managed to get rid of that annoying glitch
For the record, I asked about the map tag clutter over at Nraas (I loved the old Story Progression system of having only certain tags visible) and they said it's a feature they're considering for the future.
https://nraas.wikispaces.com/share/view/71425198