Someday suddenly above behavior occurred. If I open train menu via left-clicking placed train object, train GUI is open as normal, but toolbar is removed without warnings. So I'm not sure it is really 'removed' or 'hidden' outside window boundary. I've changed resolution after met this behavior but toolbar is not showing back though.

Remarkable changes on my HW:
Monitor: QHD(2560x1440) -> UWHD(5120x1440) but it does not related maybe. However it was fine when I'm using QHD monitor.

However I am using so many mods.

https://pastebin.com/13MpiswQ

And settings

https://www.file.io/DpxH/download/J4CbjF7FqdqM

The was a feature request to hide toolbars when trains gui is opened and restore them on close. Do they reappear when you close the gui?

Sorry for late response.
However, no. It will never reappear again as I mentioned to the original post.

https://youtu.be/8ni6x9X7pdg

It probably reepears but for some reason in the position out of the screen boundaries. Have you tried new T shortcut to bring them back to be sure of that?

Oh. That was the solution. It worked perfectly. Thanks for advice. Closing issue.

But it should bring back toolbars when trains gui is closed. Will look into it, maybe wube changed something.

Once it restored by shortcut key, it will never disappear again. Maybe changed monitor from 2560x1440(16:9) to 5120x1440(32:9) at same save file issue I think. Not common issue maybe?