[wow001]

We have exported a mxs file from Cinema 4D to work on in Studio
Problem:
All Objects have their uv sets to "locked", un locking removes previously applied settings.

Why??

[JDHill]

All Objects have their uv sets to "locked", un locking removes previously applied settings.

That is correct.

Why??

'Locked' means that the UVs are baked into the meshes themselves, rather than being dynamically generated by a 'projector', as will be done by Studio after you have switched to using one of its projections. As I recall, it has come under discussion whether or not the 'locked' UV array(s) should be stored away by Studio when you switch to a projector, so that you could then put them back again if you change your mind later.