After my upgrade from J-F cleared for JNB-FRA, UA sent me an ominous “call us regarding your ticket” email. (FRA-LAX cleared at booking.). I’m not sure exactly what the agent did, but he had me on hold for close to an hour while he worked out whatever issue it was with LH. He said that I shouldn’t do online check-in. I should check in at the LH ticket counter. My reservation looks good on the UA and LH sites, so I will follow his instructions so as not to mess up my upgrades and sc*** me out of a duck. But, yeh…weird that I wouldn’t be able to check in on the LH site. At least forewarned is forearmed!