Your ice this winter looks not too bad at all compared to "normal" Colorado ice and snow. I would expect you have had worse several times over the last decade?
You say this is your second winter in a row with a fish kill. Any chance your pond has been at maximum carrying capacity of fish for the last two years? Have you been culling significant fish from your population based on what your sampling is showing?
You may have a lot of oxygen consumers below the surface.
Hopefully, after your rescue efforts, will you will still have a lot. However, you may need to evaluate your pond population this spring.
