What’s the bracket ensemble type set to in Layout Options? If you delete the bracket/barline change at the start of the flow (the brown signpost) what happens?
If neither produces a better result, perhaps share a cut-down of the project so someone can take a look as that’s probably not expected.
I’m having this problem as well. My brackets are fine in Page View and in Engrave mode, but in Galley View they are gone and all staves are separated, which is rather annoying, to be honest. My settings are correct in Layout Options, as far as I can tell, and I have not changed them from when everything looked fine.