Navigation menu disappears when querying by category_name

I usually just use the query builder but I’m attempt to create a filterable looper using query string and feeding the category name into it. I followed a that was linked on similar posts for sorting queries without plugins. I seem to have this part working fine aside from when I actually apply the filter it’s making my navigation menu in the header disappear. Not sure what I’m doing wrong here to cause that to happen.

I have a custom post type named installations. I currently just have 2 placeholders in there. One with both categories assigned, and the other with just the one (so I can test that the looper is filtering via query).

By clicking on the terms above the results it should filter by category name which it does buuuuuut then this happens…

The main navigation disappears whenever the filter is applied. I have no idea why this is happening. Url returned is /installations/?category_name=Pews as an example. I only have one header and it’s assigned to the entire site. Have I encountered a bug or am I just doing something really obvious and stupid?

Thanks in advance!