Online checkin of UA codeshare flight operated by NH
So I hate codeshare flights with a passion, but had little to no choice to fly on one recently. It was a UA marketed/NH operated flight, connecting to a UA flight. I wasn't able to use online check-in on the NH nor UA apps. Is this the case for all codeshare flights, or something specific to NH/UA? I thought I had done it before with either a TK or LH operated flight marketed by UA.