Michael, another interesting fillet puzzle.

I will write here so as not to produce topics.

So solid on the right.
I add some fillets to it and get such a solid as on the left.



Next, on the solid on the right, I CAN continue doing fillets (red, top)
And on the solid on the left - I don’t know why - I can’t make a single fillet anymore (even on the upper edge, like on the right)

Question - what did I break?