Grid Isotope messed up Portfolio Grid layout

Can anyone tell my why after adding the below grid isotope plugin (https://isotope.metafizzy.co/faq), my portfolio grid goes from 3 columns to 4 with the last one empty? How can I fix this?

https://calliope-hexahedron-e848.squarespace.com/portfolio
Password: Square

I tried adding the below code which worked when it was static but it messed up the transitions (video shows) so deleted it.

#gridThumbs .grid-item, a.grid-item {
position: relative!important;
left: auto!important;
top: auto!important;
  min-width:100%!important;
  height:auto!important;
  padding-bottom:0!important;
  overflow:hidden!important;
}