Not entirely unexpected.
This visit was "too soon." Keep in mind that North Korean and Chinese optics are important, as well. An American president coming along, smiling and getting his way all the time puts out the idea that the U.S. is dragging everyone around by the nose as an autocracy.
Weather report: Storm.
The countdown has holds built in.
There were plenty of things that made this feel a bit too soon.
Like Q said "you will learn why in the coming weeks." Everything is set to a sequence, and while some things were lining up, some things were just not nominal.
Which means a hold would be triggered until they all got on the same page.