Wow, you may have been victim to one of the things we warn about but seldom see. If you get your ammonia dosing up around 8ppm it will encourage the development of a different species of autotrophic bacteria that's not the one we want. What happens is that it makes it more confusing because this bacteria also processes ammonia, so you think things are ok, but then when you correct the error and the ammonia levels become lower, this species can't tolerate the lower levels and dies. Then there is a period when the biofilms this species has created need to deteriorate and free up spaces for the Nitrosomonas and Nitrospira that we want growing there, so, theoretically, the regular dosing at this high level could cause a slowdown in your overall process.
The thing is, though, you can't really know any of this for sure (without setting up a multimillion dollar university lab, lol) and the only reasonable action to take is to simply correct your ammonia dosing. You wouldn't want to start over with new media as that would probably be even slower, and there's no evidence that there won't be plenty of the correct bacteria in there also, so you just have to drop back down to 4-5ppm and then just continue carrying out the correct process for fishless cycling. I just wouldn't worry about it either! Maybe it won't have been a problem anyway!
How many days are you into your fishless cycle and remind me, have you had what seemed to be a "nitrite spike" phase? (or I can go back and read at some point,lol)
~~waterdrop~~
