With increasing frequency, I'll do Save As to save a docx, I'll name it, save it, but the name I gave it is not in the title bar (it just stays "Document(number)"). And looking in the file manager shows the docx indeed didn't save. Sometimes I'll have to try to save it 3 or 4 times before it finally will. I'm not doing anything different, it just eventually saves like it's supposed to.
I would recommend you either repair or reinstall Office on your device. Please, follow the link below for further instructions. I have seen this issue before and normally a quick repair will sort it out.