Have Split Pull Rates Changed?
Split pull rates have always been a bit of a mystery. The generally understood rates were never officially published. We had fan published rates for a long time, but only very sparse official comment on rates.

Experientially, rates always seemed more generous than the initial fan published rates or the more recent rates below.

However, if you've noticed a change lately, you're not alone. Several players have expressed similar concerns on social media.
Rates changed on August 20th
LaurenWhatevs on Twitter investigated and the results were surprising, to say the least.
Using data from community members, Lauren found major drops in rates of Ink, Gold, and Kirby Krackle splits after the August 20th patch. Gold rates dropped by about 21%, while Kirby rates dropped even more sharply by about 34%. Gold went from about 23% to 17%, and Krackle dropped from 24% all the way to 16%. An ultra-desirable split combination of Krackle alongside either Ink or Gold is now 59% less likely.
These are pretty steep drops and will be easily noticeable to those chasing particular splits. Personally, I felt like my Kitty Pryde was being especially stubborn in giving me the perfect combination. If I'd known the rates had changed so dramatically, I probably would have used those credits on another character that I didn't have ink or gold finish for yet.
There is also the possibility that rates will change yet again when new datamined finishes and flares are introduced to the game.
Final Thoughts
We're not sure why the rates have changed, but it's confounding that Second Dinner would make such a change without communicating it. The implications are significant. The change in pull rates for desirable splits could easily impact spending habits and choice of which cards to devote resources towards splitting. The issue isn't how high or low the rates are. Rather, it's that they've changed without any notice. Hopefully the rates are changed back and affected players are compensated in some way.