Frames not chaining, why?

This Dorico file was exported via XML from Finale. I’m including a PDF of from the original Finale file. It took a bit of figuring out to get the Dorico version to look mostly like the original.

Just experimenting, I tried to make the page 1 frame smaller to force part 2 (the third system) onto the second page, but instead the staves and systems on page 1 simply squeeze together. I can’t figure out what Layout or other setting is preventing the third system from moving over to page 2. Any insights would be very helpful.
Harmony-WB-02.dorico (1.0 MB)
Harmony-WB-02.pdf (88.2 KB)

I would suggest creating a frame break at the start of the third system.

Thank you Daniel, that works nicely.