SQL Server: Slow restore from SQL 2014 DB, but Fast from SQL 2016 DB via SSMS We are chasing an odd problem.

We see a significant perf delta when restoring via SSMS, but do NOT see the delta when restoring via TSQL.

When we restore, using SSMS, on SQL 2016 from a DB created on a SQL 2014 instance, the restore is really really slow.

But, on the same SQL 2016 DB server, when we restore from a SQL 2016 instance, again in SSMS, the restore is super fast.

The SQL 2016 system is a super fast system, all-SSD, etc. It should always be fast.

To address, we applied all OS and SQL patches and updates to the target system. Problem was not changed.

Why would restoring a SQL 2014 DB be so slow?
The restore from 2014 is an upgrade, not just a restore.  You should actually see this in the messages window, assuming you are using T-SQL to do the restore.   You don't mention what Fast and Slow are, or the differences, such as 5 mins vs. 5 hours, so we can't add much to this.