I’ve made the switch to Gutenberg within GP premium but I’m having issues with the gallery on Safari (it’s fine on chrome). The layout goes haywire – all the images are bunched at the top covering the copy.
I’ve taken a screen shot but can’t seem to be able to upload…
9.12 is really old, there were a lot of flex box issues that were not resolved until v.10+ which sounds like the issue you are having ie. the flex container collapse.
The good news is they look great on my Safari v. 12 – so yes i would update Safari ๐