Just as a point of fact, the spawn streak denial code has been a part of the PC/Mobile in the Adobe version of game for about two years now (see below). Different codebase means that they had to write new code for Unity for the spawn streak breaker, and it was inverted for the first week of Unity release on PC, causing spawns to pretty much never fail after one extra turn. It is not a part of the current console code and the code they are tweaking now is part is going to be introduced to console in the future according to @Saltypatra.
From context, I can tell that they are hoping to back away a bit from the Justice/Mab meta by introducing the spawn breaker in consoles since without it, it is common to get spawn streaked to death by this team if you let it cast once. However, I think this is ignoring the larger issue that the Unity codebase itself (more generous with mana, bigger cascades on both sides) and the design of the troops is what makes this possible in the first place. A situation where a spawner has, for example, 70% chance to hit on a given board, without manipulation, then whatever reduced or increased chance based on how it mods the board from there should naturally streak break itself either by not getting enough mana, clearing out too much of the board for lower chances on subsequent casts, or just hitting that bad RNG. The issue is when the magnitude of effect on the spawner is such that a natural streak break often won’t occur until after the game is already either finished or unwinnable and the spawner will continually refill itself. Applying the same arbitrary extra turn limit before going into critical failure territory as if they all spawners get the same out of a cast just doesn’t make sense from a logical standpoint.
In my experience, the current state of things is first casts are more generous, second and third casts are about equal or maybe a bit less, and beyond that you better have 2/3 the board filled. My experience with the Adobe version has always been that “priming” by getting a lot of your color out by means of converter would greatly help the chance of your streak continuing, but Unity just doesn’t seem to work like that. Basically, I never “felt” the presence of the spawn streak breaker on Adobe like I am now (though I didn’t use spawners that much, admittedly), the distribution of gems didn’t seem to change so drastically and so quickly. If I did use a spawner, I would prime the board as best I could, then hazard the cast. How it “feels” on the current Unity version is that the amount of extra turns you have taken is far more relevant to your success with a spawner than the number of gems on the board, which is far too heavy handed for my tastes. How it feels is that you want to intentionally break your turn and start a new one before casting a spawner or it will blow up in your face, which is exactly the opposite of how I’d want to use a spawner - spending my time taking all the 4/5 matches off the board, intentionally breaking my turn on a skull or something, then using a spawner cast when I get my turn back. Coincidentally, this is also how the AI will play sometimes, which may be why people notice them getting better spawn RNG. Of course, part of this still may be personal bias based on the information that I have, so take that as you will.
At the very least, I’d like a disclosure of when the spawn streak breaker triggers and why so I can at least plan around it. It pretty clearly to me works a bit differently than described here by @Sirrian: