Using v19.6.2.
I have the following order:

And the reagent optimization calculation is wrong:
-
Max quality set to 5, it shows reachable is 3 with the following reagents:

-
Max quality set to 3, reagents changed from the previous one (that also says 3):

-
Max quality set to 4, now it shows that it is in fact reachable with a third set of materials (which is in fact the correct set):
