yesterday we noticed that some devices running Chaos Calmer 15.05 weren't able to download certain dependencies after boot since it seems that all files/directories in http://downloads.openwrt.org/snapshots/trunk were moved/deleted and the server is answering an HTTP 404 error.
Do anyone knows if this is a temporal issue; and in that case, when is it estimated to become available again? Or where can we find a mirror of the missing repository?
I have a question. Why do you want to use packages from a trunk snapshot on 15.05?
That URL was never a repository to a release. SNAPSHOTS/TRUNK refers to a development build. Any packages found there were obsoleted when the kernel was bumped in that trunk. You will have to install a released version to have a permanent package base.
This is not temporary.
I would suggest you use 18.06.1, though.
In the future, do not rely on development snapshots for long-term use.