Guust

You have to use HTML characters to prevent such errors, or fix after using the WP admin area.
The HTML character would be
& u u m l ;
without the spaces (if I do not use spaces here, it will look like this ü )

http://www.ascii.cl/htmlcodes.htm

It looks like you have customized your GD core files, which will always be overwritten at every update. Have a look at your child theme’s functions.php file, from line 8 to 10 it is explained changes were made to the core files, although the reference to the line might now have changed.

There is probably a better way to do this, let’s ask Paolo.

Please post your URL and admin details in a private reply and we will have a look for you.

Try this:

body.custom-background {
    background-image: url('/yourimage');
    background-size: contain;
}

Can you also post your admin details in a private message please.

“Places” is the main category (GD listing) page, so you need to have that. But I am not really sure I understand what you mean?

A coding error in one of the fields or a bad address, might do that. I cannot guarantee that is the error though.
I also just spotted that a lot of places have no category, that also will cause troubles, they just don’t know where they belong.
I would set all of them to draft, and then start turning them on block by block until you find what is causing the trouble. First set all places without categories to draft or give them a category.