Please deactivate all the plugins not related to the theme and switch the parent theme, check the issue, If the problem has gone, activate the plugins one by one, checking the issue to detect which one causes the problem.
if the problem remains, even after the plugins deactivated, please provide your site admin access to the private area.
I have checked. For now, the portfolio page works in the following way: if you have, for example, 10 items on the page, filter sort out these 10 items among the first categories, and other filters are empty as 10 times have been already shown in the categories tab. You need to increase the number of items on the page to make the filter work correctly.
Our dev team is working on this functionality to make it more convenient, however, we do not promise to provide an improved solution in the nearest update. Please increase the number of items on the page.