What you were expecting to happen, and what actually happened?
If I match 3 gems, I get Mana Surges proportional to the Surge percentage I have for that color. If I match 5 gems, I get an automatic Surge. However, if I match 4 gems, I never Surge. I’ve played thousands upon thousands of matches and I’ve never once seen a Mana Surge on 4 gems. There’s no indication (tooltip or otherwise) that this is the intended behavior, so I assume it is a bug.
What are the steps to make it happen again?
Play the game, make any 4 match. Absence of evidence is not evidence of absence, but statistically speaking, over 10 matches with even 50% Surge chances, the odds of not seeing one Surge are about 1 in 1,000 if Surges follow 3-match rules.
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!
None needed, self-evident via normal play.