Yes as Leanne noted I have the same problem: reference types disappeared from output styles could not be re-added.
Called support and they acknowledged this is a known bug with the latest update on Macs (9.1.1). They sent me a link to roll back to 9.0 which is what I am going to do.
To be clear, they acknowledged the inability to edit was a known problem. The tech was a little less clear whether the problem of reference types disappearing was a known problem. She suggested I might have done it myself by mistake, so I was glad to be able to show her that I was not the only one who had reported this. The idea that I would have an output style with only one reference type (which is what I do have now) makes no sense as I use 5-8 in almost everything I write, the same 5-8 and only the format differs.
At the end of the conversation she seemed to acknowledge that this was also known.
Of course the rollback will not fix my output styles that had reference types deleted out of them. I will have to fix them myself.
If you don’t have access to your original installer, support can send you a link.
Good luck.