Can't change the filament any more

Hello,

I did it as usual, in the last window, where the yellow one is always displayed (why?), I selected the black one and this little box that was yellow remains 2/3 yellow and the rest becomes black (I still don’t understand that either), normally when I go on, the string to the black one is then thick, but that didn’t work now: the yellow one remained thick.

After a lot of trial and error (I can’t remember exactly what I tried, I didn’t document it) it suddenly worked without me being able to understand why.

Kind regards
Proape