Check for 24 vdc between PC and 24D, you should have around 28 vdc. Is there a capacitor between those terminals, if no cap, you should install a 50volt 250microfarad cap to pick that voltage up.

possibly looking at this wrong way. Majority of times I've had the button bases crack and cause this same thing.

Boa might have it, does the car sit with doors open, same floor all the time.

Could be a bad Ground connection almost anywhere. The old TTL. DTL, logic was very sensitive to that with the gates.
Also a radio transmission very close by does strange things. Anything new installed in Machine Room?

The earthing is a good point and might be the first thing to try. When ever this is a possible fault I just place clip leads to earth at a few places in the shaft to check the effect. It might be getting a supply because of a floating neutral.

Both PC and SC originate at the center tap on the 24D transformer. Measure voltage from PC to the center tap. If the voltage is over .2v, run a second wire from the center tap to PC terminal.

These are all great suggestions, I haven't been back to the building yet but I will be and will update based on what i find.

Just in case anyone is still reading this post, you will probably find that the zener diode for that floor has started to get week and is passing enough power to fire the call. The zener boards typically have what looks like 8 regular diodes in a star configuration. You can't test a zener with a multi-meter, so to test them, just swap the wires from those floor buttons (car, hall-up, and hall-down) with a different floor and the ghost calls should follow the wires. Or, for the cost, just replace them.
Good luck!

Just had it happen, ghost calls, car and hall calls. WTF....Checked PC to 24D 27.2vdc, SC to SP 5.08vdc, PC to 9vd 15.9vdc. Didn't think it to be cracked bases, unless some jerk beat up every button. Got a rack of card's available, so I'll start there. Nope that really changed things for the worse, SC to SP 5.06vdc. Car now wont answer any calls, as a matter of fact it only runs up when the hall call on the bottom floor is pushed??? Start putting old boards in one at a time till that goes away. Back to ghost calls, thats better. Car now goes to 2 then down to 1 then up to 2 and the door are jacking off. Is this the real problem? It only does it on 2. Go check DCL, barely making, check door linkage, adlust it back to where it belongs, yeah thats it, nope still jacking off until it got a demand to run, then it would answer that call and go back to 2 and you guessed it. This car has no homing. While in the door op I did notice that the gate switch contacts had moved to the outside of the ring, of course they where loose, adjusted them to make at close. To conclude, the gate switch was the problem all along. It quit going back to 2. Getting a new rack of cards as these can't be trusted any more. My option card has 6 slots but the rack only needs 3. Did they ever make a 6 slot controller?

I know they had 4slot bds, if not mistakeing option bds sometimes had more slots depending on versions. I've always been told that newer versions, the ones with more slots, can replace older ones directly but not the other way around. You should be ok. I want to make you aware that the 5.06vdc should be between 4.8 & 5.0. Don't think +.06 volts would matter but you never know.

The card that turned it for the worse was the car card? But the Ghost came back next day. Went over screw terminals in car and controller, Loose ground in COS, also cleaned IN3 contacts 2/4/8, SC side of card rack. Been good so far. I'll keep all informed if it lasts. Good Day. Work Safe.

Still running strong (as they usually do) Not a problem with it since. Thanks for all the suggestions I got from this post and all involved.