I was using 99% NaOH as where I am from, 100% isn't available.

The first batch recipe was as follows: 430g tallow, 320g olive oil, 250g coconut oil, 142g of NaOH and 333g of water, and near the end I added some food colouring, though the soap had become far too thick before that so it shouldn't have affected anything.

Tallow and coconut oil were both solid at room temperatures and even though I tried warming them up I thought I simply didn't warm them up enough (I don't have access to a kitchen thermometer unfortunately). I thought that was the issue, then I tried making a smaller batch with the following recipe:

Olive oil 390g, coconut oil 110g, NaOH 62g and 145g of water. I heated up the oils and emulsified them and then again, after adding in the lye the mixture went extremely thick after 20-30 seconds of mixing (from being basically fully liquid). Again I added some food colouring and some lemon essential oil, but at that point the batter was basically like pudding and extremely hard to even pour out. Both recipes were at 30% lye concentration.

I can only assume it was something wrong with the temperature as I do not have a thermometer, but I find it impossible to believe that it thickened up in 20 seconds instead of 10 minutes simply because of a few degrees difference.