I would guess it overheated. The sugars in the milk tend to make things warm, and also they can scorch with the heat of the lye-water reaction. Most people will freeze their milk before adding the lye to avoid it heating up so much. Lye and water combining is a HIGHLY exothermic reaction (produces a great deal of heat) and can be really dangerous if you warm liquid before adding lye to it. It could boil out of the container and scald you, as well as give you severe chemical burns from the high alkalinity. Not to scare you, but it's incredibly dangerous and I'm glad nothing happened to you with this batch.
This is not a very well-balanced recipe. I ran this through a
soap calculator (
soapmakingfriend.com) and came up with a 14% superfat, which is ok with 100% coconut oil, but with the added beeswax it might have caused some issues. You have to soap pretty warm with beeswax otherwise it has a tendency to set up faster than the other fats and separate out. As Obsidian said, you've used 14.3% beeswax in this recipe and that is far far too much to make this a decent bar.
It probably thickened up fast because of how much beeswax you have and also the amount of coconut oil. CO tends to move pretty fast and the beeswax definitely did not help things.
I also want to touch on the stick blending for 5 minutes thing - that's gonna be way too much. You'll want to watch how much you blend if you want to have any workability with the batter while it's fluid. It can be helpful to watch some YouTube videos of people making soap so you can see what their batter looks like when they start to work with it. Royalty Soaps is one of my favorites. Beginners are often recommended SoapQueenTV but she tends to only promote her own product and uses glass/Pyrex bowls which can be dangerous with the high alkalinity - so take those with a grain of salt.
As Obsidian has said, let us know what oils you have access to and we can help you develop a better, more balanced recipe! I see you're in the USA - you can buy plenty of oils and supplies locally at a Walmart or something similar for pretty good prices and make lovely soaps. A recipe similar to mine that I suggest:
45% lard/manteca
35% olive oil
20% coconut oil
5% superfat
33% lye concentration (not water as % of oils if you're using soapcalc)
You can find all those fats in the baking aisle of Walmart and it should give you plenty of working time even if you over-blend a little. Freeze your milk into cubes and add the lye granules s l o w l y and stir well. You can put the container you're mixing in into a bowl filled with ice water to keep it even cooler. I suggest starting with plain distilled water for a few recipes before you graduate to milk soaps. It'll help you get the hang of the process without having to worry about what temperature the solution ends up at - the water won't care if it gets hot!
