No close [x] button in app windows

[Jonathan Lumb]

Occasionally, the close button is no longer displayed in the corner of app windows. This means I must use Alt + F4 to exit the app. When this happens, the font used in apps also looks different. To resolve the issue, I must log out and then back in again.

Screenshot attached.

Thanks

[Jonathan Lumb (jonolumb)]

The open file window also changes to the following layout (see attachment)

[quassy (quassy)]

Have you modified the theme in any way?

Maybe this helps (it resets the window button layout to close left, maximize right):
gsettings reset org.pantheon.desktop.gala.appearance button-layout

Is this the open file dialogue of a particular app or any does it happen with every app?

[Jonathan Lumb (jonolumb)]

No - I haven't modified the theme. This doesn't happen all the time - it seems that some process is crashing, which is causing windows to change. The open file dialogue is like this for all apps after the 'crash' occurs.