That specific part of the website uses your theme. Anyway, the issue also occurs here on your theme website:
https://seatheme.net/demo/art/html5-template/portfolio-grid-10-standard-col4-text-filter.html
if you make the window small so that only one item appears per row, then reload the website and press the filter, anything that has was not visible before pressing the filter appears grey until the scrolling is used. Would it be possible to add code that loads anything that becomes visible as part of executing the filter?
Thanks!