The only thing I can think of for when this happens would be to right-click on the part or sub-assembly in the tree and choose "Component Line Font..." from the drop-down. That will take you to the dialog box shown below. Un-check the box for "Use document defaults" at top left, and then you can change the settings for the selected component. Be aware that if you leave "All views" selected at the bottom then whatever changes you make will affect all instances of the component in the drawing. If you choose "From selection" instead then the changes will only affect the selected component.
Unfortunately this doesnt solve the issue .
In my opinion it could have something to do with the gfx driver of card or something with thte system as sometimes all it needs is to be deleted and re-inserted in to the drawing space and it works.