When on a large multiplayer map and making a large blueprint that involves trains the UPS hit can cause the server to time out all players for a minute as it processes the BP. The server is pretty high end and we have gone to the edge of the map on it (1 million tiles) before.
Example BP that caused this: https://pastebin.com/ctyiG1LN

Is there anything that can be done about this?

To clarify, are you creating a new blueprint or building an existing blueprint?

Holding shift is the reccomended way to create a blueprint.

Creating a new blueprint is when the server Max's out cpu.

We don't want to include the trains that happen to be there at the time.

In the MP game there is no disable train blueprint button like in SP. I am an admin in game. Is this a bug?

Missing blueprint train button is a bug.

I tested that the button shows in multiplayer with Blueprintable Trains as the only mod. I guess one of your other mods is causing a conflict. The button uses the "mod-gui" API.