From the Priority Club website:
Airport: Orlando (FL) - International (MCO), Terminal B
Lounge: UNITED CLUB
Note: Members holding a Priority Pass Select membership card and Priority Pass cardholders in the U.S. that receive their membership through a U.S. financial institution will not be allowed access to this Lounge.
What a bizarre carve-out! I suspect that's a capacity problem and also why the DL lounge left the scheme