I noticed you were rather vigorous with the mixing. You also poured the epoxy with some kind of measuring jug from the spout.

I am sure I read somewhere that poking a hole in the bottom of a container and using that to pour is a handy way to do it. It allows any bubbles that have formed in the 'gentle' blending of the two part epoxy to rise to the top. Stopping an aerated mixture being applied to the frame.

Also, it might be worth a try with the extra slow tropical hardener?

My thinking being the longer cure time would allow not only the bubbles to rise for the bottom pouring method, but the heat gun to work to release bubbles as the epoxy remains less viscous for longer.

I've never poured either. I am just repeating what I've seen other people have success with on this very forum.

Hope your next pour goes better.