When migrating to Mojave or fully reloading a computer with a fresh OS install, Migration Assistant fails to prompt for the key for an encrypted backup, and sofails completely.
This case arises when running the lastest OS on a Synolgy NAS (DSM 6.2.2-24922), which worked fine under 10.13.
The work around is to:
1) set up the mac as new.
2) connected to the synology back up NAS
3) locate and click on the relevant time machine backup
4) provide the encryption key at the prompt
5) run Migration Assistant
6) select the timemachine back up as the source
It is quite incompetent to have restores broken for encrypted backups this far into a release. (Everyone with a clue uses encrypted backups.) There are obvious Q&A problems.
Then again, Mojave has been riddled with serious bugs, so maybe the development process and code review process are broken, or apple is outsourcing.
Given the continuing vulnerability of the mac platform due to lack of memory safe hardware, failure to use type safe languages, and bloated code due to poor abstraction, frequent full resets of the entire platform are necessary to flush out compromises. This means reloading from backups will be done with high frequency. So, it surely ought to work!