Solved Z offset stopped responding all of a sudden

I'm not sure why this happened out of the blue, but for weeks I have been having no problems with the z offset. I'm using a Robo 3D R1+ with Marlin 1.1.0 RC8 with mesh leveling, and I was able to set it on my LCD screen without problems. I could make minor adjustments and notice them right away. If I wanted to save the settings, I would send an M500. Now, out of the blue, no matter what z offset I set, the nozzle remains at about 2mm away from the bed. I had the z offset at 0.72mm before and I was getting a perfect first layer. Now, even if I change it to -2mm, the nozzle does not change position when it starts printing. I have NOT made any changes at all. It just started happening. I have tried M500 a dozen times (even though it's not required unless I want to maintain the settings after I shut off the machine). I have tried M502 then M500, then re-doing the mesh leveling (about 5 times), but no luck.One thing I did notice is that the Pronterface terminal always says "Z offset: 0.00000" when I type G29. I think this is normal, but not sure why it doesn't state the actual z offset.
Also note that I have not changed anything in the custom G-code in Slic3r. The order is exactly the same. None of the settings in Slic3r have been touched. The Slic3r Z offset is set at 0 under "Printer Settings". I never change that. I have not had z offset issues until today. I'm just looking for other ideas.

 

Thanks for taking the time to respond.
Ok, so you're right, in that G29 S4 Z.n.nnn did in fact change the "Z offset" in the terminal window (after I type G29). However, on my LCD screen, it doesn't update the Z offset, but rather the "Bed Z". The Z offset on the LCD screen remains the same. I know we've talked about this before and you mentioned it's probably a bug in the firmware or something. However, using the G29 S4 Zn.nnn command did actually adjust the nozzle height from the bed and allowed me to print successfully again. However, it doesn't quite explain why adjusting the Z offset from the LCD screen just stopped working all of a sudden, and I've been doing it for weeks. Oh well, such is the life of a 3D printer user.
Again, thanks very much.

 

Oh I see. Good to know. It's amazing how much one learns when things go wrong.