In Standard and CtB, the gold medals can be earned through achieving a "Perfect".
This means to achieve maximum possible combo on a given map - for these two modes.
I think the problems are different for Taiko and Mania:
In Taiko, the maximum combo is well-defined for any map, but there is nothing called Perfect at all. Even autoplay result does not show the Perfect message.
On the other hand, in Mania, any play with zero 100's, zero 50's and zero misses counts as Perfect, but the actual number of combos can differ.
These points must be considered to make the gold medals work correctly.