So If you check in 3d coat V 4.9 from Top menu >Edit > Relocate data path, then just copy the path in text editor,
it may show default 3d coat data path for V 4.9, and for V 4.9, add on need to set Exchange directory as " the data path/Exchange" for 4.9 work.
After you check V4.9 data path , check blender scene which you plan to export by applink add on. each exchange path save with scene.
then if it was wrong, set again. and save new exchange directory> save the blender scene> try select mesh then export.
When change Exchange path for add on, then try to export , it sometimes take time untill import dialogue open.
(sometimes freeze with import material menu open)
but usually shut down 3d coat, then run again, and export again , should solve issue. Once the new exchange setting work correctly,, there is almost no issue for me.
without you tweak 3d coat to blender export setting (when return mesh and material from 3d coat, it need to keep some option or sometimes it fail then only generate custom 3d coat nodes.