Oh dear, that's no good :(
Would you mind following these steps and share the outcome?
- Hover over the locomotive that is not showing up
- Press Ctrl+Shift+F (this should bring up the prototype window)
- Search for "flag"
Or if Ctrl+Shift+F does not show up the prototype window (could be because another mod overwrites this)
- Press Ctrl+Shift+E
- Search for "locomotive"
- Open the locomotive prototype under "item"
- Search for "flag"
The resulting screen should look something like this: