Hi,
It is not suggested to remove MappingRandomizer from BaseColor slot of material or not have it at all - this was mentioned for identifying for anyone interested where the issue was.
The issue is when such material is previewed in the viewport - mapping randomizer is not going to be previewed in the viewport fully anyways (base texture with simple tiling is previewed), so just disabling the material preview will be enough.
By the way - this case was scene/material/object specific (not able to reproduce in a simple scene) and was exactly because of CoronaColorCorrect > CoronaMappingRandomizer > BaseColor slot (without any inputs, any of them) for a material, which is previewed in the viewport (probably for these specific objects too). A new material from scratch was creating like mentioned, and the viewport was slow.
But what is the strangest part - if the same material was applied to ALL of the objects in the scene, the viewport was fast, from 5 fps to 90fps...
Even if the original user submitted material was applied to all the objects in the scene, the viewport was fast... but not if applied to the original objects.
It was a very strange scene indeed.