Technically you're not actually checked in until you get onsite IIRC.

Mobile check-in basically lets the (fill in the blank) property know what time you're arriving, if you've got requests, etc, & they'll have the keys made, hopefully have fulfilled the requests & ask if you want to use the CC on file when you arrive & then check you in. If someone paid for the king casita suite, then yes they can take away the free upgrade as it's based upon availability (not sure how that works w/ SNAs).

Know someone who had a suite upgrade at JW in London. Showed suite when she was getting on plane to fly to UK but got a non-suite room when she arrived because a US professional sports team that had been staying there had extended their stay by a day & they had booked/paid for the suites, so no longer available for her.

FWIW - can't hurt to ask upon arrival if a casita is available. Someone might have canceled by the time you arrive.

PS - I believe there is a property thread on Triada, so after your stay please do a trip report. Thx!

Cheers.