Image is missing for some periods of time

See this issue https://github.com/Shippable/support/issues/3392

I believe the root cause could be that when a new build is in progress, the old image is deleted.
What if there would be a possibility saying that “I want the image even if it is a bit behind”?

for anything else than experimenting, you should stick to tags. Would this be an option for you?

You also can reduce the problem by reducing the number of layers you are using. Your Dockerfile currently uses too many layers. Combine all Run Steps into one would ease it.

You currently also have a single Run step for apt-get update. This is dangerous. You should not do apt-get update and apt-get install in two different steps cause due to caching it could happen, that the apt-get update is outdated once you are installing something.

Hope this helps a bit.