If the diopter is correct (i.e.the green characters look sharp) then:
1. are you inbright conditions trying to focus on a subject with good contrast?
2. when you say only one or two focus points light up is that when you have it set for all focus points active or when you select one focus point and move the selected point around the viewfinder? (It's not uncommon that all points don't ligt up since maybe only one or two find a subject to focus on.)
3. If the green chatacters are sharp and the focus points aren't did anything happen to affect the focusing screen?
" I have checked the diopter settings and that is perfectly fine."
I doubt it. Do a critical check again. If you wear glasses it may be more difficult. Plus the diopter has limits to what it can adjust. You can get additional diopter support for the eyepiece but I don't know it is available for the T5.