I think the simple answer is there was a scheduling conflict. Jennifer could only film for certain days. Lana wasn’t even ever on set with her and they are supposedly in a scene together. I think they then had to create a reason why Emma wasn’t in the early scenes and why she didn’t just come along right away when the real reason is that she was only filming for a couple days and they decided to just not have her be in the first few scenes in the Enchanted Forest.
I think they couldn’t figure out how to have Henry talk to Regina and how to have Hook wander off alone and have fake Hook come back if Emma had been there. The writers are just not very good and the scenes were choppy and the dialogue was bad.