The DS716+ and DS216+ models received an update to DiskStation Manager 6 this past week. The only change was to Improve the stability of system boot up on these two models and this update has not appeared on any other Synology Models that I support. I didn’t have a problem installing it on the DS716+ although I don’t have access to a DS216+.
The one DS716+ I support never got DSM 6 Update 3 even though it is listed in the release notes. I assume this update contains the previous fixes from Update 3 since it happily skipped that update.