Asked the devs for help via posting on the LoH forum and via private messages here.
In the end we couldn’t figure out what had happened, fortunately they were able to figure out what my class badges had been. (My regular skill badges were fully intact; it was just the class badges that were gone.)
They couldn’t directly reinstate the badges for me, but they figured how many SPs I would’ve needed for them, and they gave me that many SPs.
Give them as much detail as you can because they have no idea what causes this and were quite distressed that it happened without them understanding how or why.
I was without badges for maybe 3-4 days after I asked for help but I am very happy with their response. I hope they’ll look after you too.