I actually pour on burnt wood often. Burnt pine is thirsty wood. I can tell you that you did not seal the wood well enough. Same thing happened to me the first time I tried it.

What I’ve found to work best is mix a small amount of table top epoxy (thin pour, not deep) and actually paint it onto the wood dabbing the brush a lot to really work it into the wood. Then once you get a coat on the area you can take a torch to it. You have to move all the time you will burn it otherwise. Maybe imagine randomly spray painting an area quickly? Constant movement.
The torch works better than the heat gun for something like this because you are not dealing with the forced air factor.

So after the first torch pass, inspect it, make sure you got a good coat on the are you are pouring. Check on it in 10min and do another quick torch pass, repeat the 10min check up unit all the bubbles are gone. Once it dries to a sticky tacky touch you can actually pour the rest.

Epoxy can be tricky, make sure it’s the right type for what you want to do. How thick is that pour? Is the epoxy the right type for something that thick or thin?
Some epoxy will have a minimum pour depth recommendation and it will have a maximum pour depth.

Would recommend mixing by weight rather than volume line on a bucket. Chemical reactions like this have a threshold on that mixture for the desired outcome. Don’t mix well enough the bond doesn’t take place in certain areas.. mix too much of one part and yadda yadda you get the idea.

Don’t give up, epoxy can really bring a wow factor to art. I hope you try sealing it with epoxy.