Since last Update (v3.4.5) it’s not possible to select entries for the Masonry. Tried on different Browsers, same issue. It’s now a dropdown menu, whereas it was a selection box before.
same for blog entries, can’t select taxonomies :-(
I think this is adressed here already:
https://kriesi.at/support/topic/after-latest-update-no-options-to-choose-masonry-portfolio-or-post-categories/