Regarding the postfix issue, when you update to 11.0.x, appcd initiates an apt install for the required packages. If this fails due to a network issue, package conflict or similar then it is not automatically retried.
From the control panel server, run:
appcd-cli 1.1.1.1 install-mta
appcd-cli 1.1.1.1 install-imap
Replace 1.1.1.1
with the IP of the server which has the issue.