Hi Peter,
I’ve updated Bootstrap and Masonry on a local version of my demo, but the animation is still fast enough to make it difficult to replicate this problem. I should have to slow it down on purpose to see the issue (just as you had to speed it up to see the issue).
Just come back after rebuilding my demo on my CodePen account. I’ve purposefully slowed down the transition on the .item element (both transition-delay and transition-duration have been delayed). It looks to me that the items reposition themselves even if I don’t let the animation complete. Only, it takes a bit longer because of the increased timing, which makes it look like it’s stuck.
Thank you so much for your feedback.