After effects: unable to type text in text layer

I have a very peculiar problem with text in after effects. I have text layers with text that I wish to edit. Has been working just fine for a week but this morning, after effects decided not to accept changes to existing text or to type text in a new text layer. 

If I try to select a section of the text it immediately jumps to selecting the whole text layer and I cannot change the content. I can change the size, the spacing, etc. If I try to type new text, it creates an empty text layer wihtout content - in the layer overview next to the timeline it just says "empty textlayer". Same if I try to open up a text layer by pulling it with the title tool activated (sorry, English is not my first language). 

To make it even stranger: I can select a section of the text, force the selection to stay selected by not releasing the mouse button, and type my changes. When I release the mouse, the text will show up changed. That does not seem to be the most efficient way to edit my text, does it?

Also, that little line directly under the work area, that usually indicates which section of your composition is renderd via RAM preview, keeps flickering in green. 

Any ideas? This is driving me mad, I am coming up to a deadline, and I would rather not redo 100 text layers, highlights and stabilisations in this project. Thanks a lot!