when the kiln gets too fast it resets the recipe to the basic version without fluid input even though i have more than enough fluid, around 1500-2600% speed

Thanks for the report! Tracking the issue here

I've checked in my own playthrough and this actually just happens randomly from the looks of it, even at relatively low speeds, my biggest suspicion right now is that any sort of fluid shortage causes the recipe to regress to the basic version, and then Restoring fluid throughput doesn't change it back. So it resetting the recipe could also be caused by Factorio's fluid throughput limit, since at such high speeds and because the kiln only has like 40 fluid storage, transport doesn't happen quickly enough.

The situation where a temporary fluid shortage causes the recipe to switch, but restoring fluid does not cause the recipe to switch back, is just how Factorio itself handles furnaces with item+fluid input. This is the case regardless of the reason the kiln got low on fluid.

In terms of the kiln running out of fluid just because of its crafting speed: this actually doesn't seem to happen in Factorio 2.1. I will look into getting this fixed on 2.0 too.

The kiln's fluidbox was increased in size from 40 to 100 in v0.5.11 (Factorio 2.0).