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).

Still a problem btw. Fluid dips below a certain level, recipe changes with some fluid left in the kiln (not sure how or why), kiln stops accepting anything and goes into "now I need to empty the inventory". Inventory contains only fluid. Problem is - it also drops fluid connections so it can't empty it until manual intervention. No fluid connection also means it stops passing it to other kilns that rely on though connections, knocking them out as well. Whole system grinds to a halt. Depending on how paranoid you are - it will also start exploding...

What version of the mod are on?

Most recent one when I noticed, something released within last 48 hours when it happened. Not sure when exactly it broke.

Just happened again, most recent version.

In both cases I had a bunch of consumers sitting on the same pipeline with no large buffers.

Nothing about the kiln has changed in any recent version. The new behavior of pass-through fluidboxes in Factorio 2.1 has made this better than it was in 2.0, and the devs have said they're still making changes to the fluid system; kilns are working well enough that I'm planning to wait for the fluid changes to be finalized before considering altering kilns.

There are some workarounds to avoid this issue from disrupting your factory:

• Use circuit conditions to stop kilns from producing if the pipeline is low on fluid
• Install Furnace recipe selection so that kilns will behave like assembling machines (putting rigor modules in kilns will also let you select the recipe).

Yeah, I fixed both places with circuits and added larger buffers. Should probably be sufficient until upstream fixes. Fun planet :)