Rhino 6 nothing to undo error

Hello, I am using Rhino 6 and have encountered a problem for a couple of days now. When I try to undo, rhino either undo once or not at all, saying “nothing to undo”. I have a large memory (32GB) and I have allocated 16 GB for undo operations, still no difference. Any idea on how to fix this issue, it is really annoying and stops my workflow… You can find my system info as follows.

Windows 10.0 SR0.0 or greater (Physical RAM: 32Gb)
Machine name: COCHON

Hybrid graphics system.
Primary display: Intel® UHD Graphics 630 (Intel) Memory: 1GB, Driver date: 9-11-2020 (M-D-Y).
Primary OpenGL: NVIDIA Quadro RTX 3000 (NVidia) Memory: 6GB, Driver date: 10-22-2020 (M-D-Y). OpenGL Ver: 4.6.0 NVIDIA 452.57

OpenGL Settings
Safe mode: Off
Use accelerated hardware modes: On
Redraw scene when viewports are exposed: On

Anti-alias mode: 8x
Mip Map Filtering: Linear
Anisotropic Filtering Mode: Height

Vendor Name: NVIDIA Corporation
Render version: 4.6
Shading Language: 4.60 NVIDIA
Driver Date: 10-22-2020
Driver Version:
Maximum Texture size: 32768 x 32768
Z-Buffer depth: 24 bits
Maximum Viewport size: 32768 x 32768
Total Video Memory: 6 GB

perhaps rhino>options>advanced :

Hi -

You cut off the part that says which exact version of Rhino you are running…

If you start a new file from a factory-default template and create a box, does undo then work?

Finally, that was it!! No idea how it got changed but thanks a lot!