Open website with Google Chrome on mobile device.
Go to shop category (it seems it works on the main shop page, so choose category).
Scroll down and click on page 2 for example.
Open filters sidebar (button on the left).
You will see that it opens at the bottom of the page instead of nice popup.
It works well if you are on the first page.
Only page refresh helps.
I have attached a video that shows the problem.