Pagination Error in link formation

Hi

I have a problem with the pagination in MH Magazine Lite for category and other queries that return many pages/posts.

If you go to this URL https://tracks-magazin.ch/?cat=4 it’s a query on a category that has many posts.
The red buttons at the bottom indicate 3 pages are available. However, if you hit one of these buttons you don’t get to the next posts. Instead it stays where it is. The URL being generated is https://tracks-magazin.ch/?cat=4#038;paged=2 which I think is in error.
If I manually make the URL https://tracks-magazin.ch/?cat=4&paged=2 then it works and gives me page 2.
It is happening every place that these buttons appear, and on Safari and Chrome on Mac with OS X 10.10.1

Then I did the following to eliminate any issues with images/plugins;

1. I’ve set up a new test site, no images, no plugins but still get the same pagination problem.
a. site https://tracks-magazin.ch/tracks_test/
b. The Home Page works fine.
c. The filtered list of posts (by category) does not work.

2. Now I’ve narrowed it down to the following;
a. The Front Page is set to ‘Your latest posts’, the pagination works
b. Menu ‘ALL POSTS’ is simply the link back to the front page, and also works as you’d expect
c. But Menu ‘REVIEW’ is a category menu item that will filter the posts only for that category. Now the pagination does not work.

As far as I know, I’ve got nothing customised going on this site, as mentioned there are no plugins activated and none of the additional plugins from the other site are even loaded.

Many thanks for help on this.