Hello b1izzard
Yes, this is completely normal - vSAN doesn't flush data from cache-tier devices on power-off/reboot (as that would be slow and/or risky) and essentially has to rebuild and check the metadata on the Disk-Group from data on the cache-tier (e.g. PLOG Recovery).
While this is a faster process in 6.7/7.0 GA than it was in older builds, it is now an order of magnitude faster in 7.0 U1 (e.g. seconds not minutes) and likely you won't be staring at this screen for any considerable length of time once on this build.
Bob