There seems to be a repeating pattern of 4 good blends followed by 2 bad blends. Perhaps this is just a consequence of the relationship between the animation length and the frequency with which I play a new anim.
I saw the response from @britzl that there won’t be any fixes to the current Spine implementation, which makes total sense, so if anyone can think of a workaround for this it would be great to hear.
Also realised that I posted this under ‘Questions’ without asking one - does anyone have experience with blending between looping anims like this?