I believe this is a Ultimo theme issue. The author has stopped updating the theme. I have this theme on Magento 2.3.3. Pagination Next/Previous not working intermittently on iPhone. Sometimes it works after clicking twice with no response or error in console to one click. As you can see from the screenshot taken from a iPhone that a click on page 2 is stuck with number 2 label highlighted with black color.
the example from OP's question: http://ultimo.infortis-themes.com/demo/default/fashion.html
EDIT: Did a little digging and got some more info that I guess made my last answer kind of pointless so here you go
Looks like Apple have been known to cause a similar issue when things are changed/shown during
:hover on an anchor tag. It's their attempt at being too smart for their own good by the looks of it. First click causes the hover effect, second click causes the actual click.
Kinda sucks that this is a part of Apple's "intended functionality" but there's possibly ways around it. You can try wrap the
:hover CSS in a media query to not change colour on touch devices, and there's some other little tricks I found here: https://css-tricks.com/annoying-mobile-double-tap-link-issue/