Why all my new builds failed with "chroot Problem on xx-host"

You've made gnome-flashback-classic "Essential: yes", which means that apt tries to install it when upgrading the chroot as almost the first thing the build does, and it can't for some reason. Essential is totally inappropriate for things that far down the dependency stack; it's only meant to be used for a very small number of things that form the absolute unremovable core of the system, definitely not anything to do with a desktop.

I'd recommend removing gnome-flashback-classic from your PPA using https://launchpad.net/~ghostplant/+archive/ubuntu/flashback/+delete-packages, waiting 20 minutes or so to ensure that the deletion has been published, and then reuploading it without the Essential flag set.

In fact, I see that you've already tried to remove Essential in your most recent upload, but it can't build for this very reason; you'll have to delete it first. You can use https://launchpad.net/~ghostplant/+archive/ubuntu/flashback/+copy-packages to copy it back in once it's deleted without needing to use a new version number; you'll need to change the status filter at the top to "Any status" in order to find it.

Thanks, everything becomes well!