Hi Jasper it looks like the page rules were inverted somehow. I had a "hide rule" for two pages which somehow got turned into a "show rule" (so our buttons were now only shown on 2 specific pages instead of not shown on them).
Once I corrected that the buttons came back, but with completely broken styling that I was unable to fix (button backgrounds weren't obeying radius styling settings and icons weren't responding to sizing).
I ended up having to recreate the whole button group and buttons from scratch and now it's all looking right again.
Very strange because I don't believe anyone on our side had worked on these buttons since I set them up. So am assuming they were corrupted/broken after an update to the Buttonizer plugin?