As I understand it, if your server is using SSL encryption, your clients may not be able to connect to the server if they are updated before you update the server. This is especially an issue for FM GO users as it is not easy to "roll back" an iOS device to an earlier version.
If your server is not using SSL encryption it shouldn't make any difference.
Under the "database server" "security" tab, I see that we don't have "Require secure connections" checked.
May my ignorance help someone else. Of course, they have different instructions for this scenario:
If you are accessing FileMaker Server, but have the Secure Connections (SSL) option turned OFF (located in the FileMaker Server Admin Console > ). Follow these instructions >
And it says
The order in which you install is not important. FileMaker does recommend updating to the latest versions below:
So this now leads us to the question of setting up the SSL as required and I can search for that process. Maybe we should do that when we upgrade the server and the rest of the clients.