No worries,
 feel free to visit our Discord Server and tell us the materials that you want to have in the addon and we will work on making it in future updates

All materials that has no displacement works just fine.

This is  the first version of the addon, So its normal to have some issues.

to solve the problem(if you had) reinstall the addon and install it again.

or

Send you problem on the Discord Server and we will solve it to you.

Yes as the materials are cc0 which have no requirements.