Sounds like the stepper is slipping quite a bit which means it’s being overloaded when trying to pull the Z carriage back up.
I had a problem where I would be running a 3D carve, pause to clean chips, then resume and it would plunge deeper which hinted towards lost steps when it was raising. Before I had help figuring out the problem on here, it got to a similar point where it would only raise if aided.
Turns out it was a simple matter of adding some lubrication to the bearings. Once I got some of the Mobil Vactra #2 and lubed the bearings, the machine was working great again.
Here’s the link to my problem plus documentation for lubrication:
https://community.carbide3d.com/t/nomad-3-z-axis-grinding-and-plunge/38093
Hope this helps!