1. If problems only with the CAM files - it means that there are files without these problems, for example CAD.
Therefore it is logical to compare all settings of groups and users, and Workflows. I think that it has been already attentively made. In that case I can offer to try to add (temporarily) for test files to another - the working Workflow. Perhaps it something will help.
2. To see file History - perhaps at Check In the new version / edition isn't created. To find out why.
3. Perhaps in Workflow it is necessary to choose - "to ignore permissions in the previous state".
And still there is a question what version of PDM? Standart/Pro, 2018 spX? And what Windows?