Maven's invitation Drop Rate ?

Hi, I'd like to report a potential bug regarding the drop rate of Maven invitations, at least for the Shaper Guardians
I've done over 20 rotations of Shaper's Guardians and I've probably seen 3 or 4 maven invitation drops, that's even with the allocated points for Final Map boss in each map has increased chance to drop a maven's invitation.
Before this league release I never had this problem, I very rarely had to buy any formed's maven invitation using the same strategy.

Does somebody else have the same issue or that is how it is intented to work ? ?

There is another post recently about this. My comment is they have been dropping frequently for me in the standard ruthless mode, but perhaps there has been some adjustment in the current league, or just bad rng.