In order to help you, please, provide us with the additional information:
1) screenshot of "About Folx" screen;
2) screenshot of "About this Mac" screen;
3) describe the exact sequence of actions, so we could reproduce the issue on our side;
4) send Folx feedback (open Folx > reproduce the issue > then click on 'Help' in the top bar menu > choose Feedback > specify your email address and send it);
5) send us the link to the file where the issue occurs;
6) launch Folx, find the renamed file in a "Task" window, right-click it and from the context menu choose the option "Show in Finder". Is the file renamed or not?
Looking forward to hearing from you.