We got a ticket from Biomed about their jobs not running properly.
I had a suspicion that this was the case, and when I went to the yaim tool site and found that not only had they changed their VOMS certificate, which I had updated, but they had also changed their VOMS server's DN.
So, I changed their VOMS DN in our site-info.def and re-ran the config_mkgridmap function on the CE, which also configures LCMAPS. After that things seemed fine.
One to watch out for, though, when updated VOMS certificates come through.