Hi, I am sorry for the inconvenience.
I will help one by one.
For now, Please visit MediaPress->Settings and on the General tab, Please uncheck the Sitewide Gallery and save.
That will make all the links work. currently, the shipped version has “gallery” set as archive slug and if you create a directory page and use same slug, they conflict and cause issues.
A simple solution is to either disable the Sitewide Gallery or change the gallery directory slug, or the last resort you can change the slug of the sitewide archive(but that needs permalink refresh and I don’t recommend the last options for now).
Please do that and let me know if it works for you or not?
I will be happy to assist you and get it working correctly. Also, Please do take a look through the docs, that may help with some of the issues.
Thank you
Brajesh