Gotta hand it to IBM support. They’re still investigating and they’ve provided a workaround that’s possibly better than just allowing dual reductions only. They recommend setting a parameter that I don’t quite understand: “cplex.params[1138] = 0;”. They called it “extended GUB presolve”, but by setting this parameter to zero, I would guess that I’m actually disabling something. Hopefully they have a fix out soon.