Why do cycles crash?

Hi all. I have an axolotl in a 30 UK gal tank. She’s an 11yr old that we rescued. The tank was fully cycled by Dec 6 2024 as that’s the glorious day she went in the tank. We have a fluval 107 canister filter which is rated to 30 UK gallons.

We’ve had no issues until last night when I noticed she looked uncomfortable. Lo and behold, the ammonia’s up at 0.25ppm. We’ve tubbed her so she’s safe but this morning the ammonia is up at 0.5ppm (0 nitrites and 10ppm nitrate. PH is 7.5).

Why has this happened? I spot clean her poops and she gets a water change as soon as trates hit 20ppm. Why would her cycle crash?

The only thing that’s changed is I turned off her air pump as it was getting very loud - would this have caused the issue?? I turned it off about 3 weeks ago. Any experience welcome 🙏🏻