Masonry in groups activity not working

Masonry view no longer works for me.
Previously I was running Version 4.5.4 because this worked and upgrades beyond 4.5.5 broke Masonry view (4.5.5 itself had other issues so I dropped back to 4.5.4). I’d really like to get this resolved so I can upgrade future releases.
Summary:
4.5.4: Masonry view works fine in Buddypress groups
4.5.6 and onwards: It doesn’t. Images appear large in a single column in the activity feed (but still cropped, even without size settings set).

Can anyone shed any light on this? I see a fix for image sizes came out in 4.5.6, but no idea whether that’s what broke it.

TIA

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