That looks like the package index is mangled somehow. While the base OpenWrt OS has a fixed release point, the packages follow a rolling release strategy, so you can sometimes fall into the cracks between when a package's .ipk is uploaded and when the corresponding index gets uploaded. If the servers and/or network are congested, like when, oh I don't know, there's a new release and 1000 eager beavers are trying to download it, then it can take 10s of minutes; or maybe something times out and you have to wait for the next cycle.
That's sort of hard to answer, because "it depends". The ASU server keeps failed build status around for 10 minutes (i.e., if you submit an identical build request within that window, it will return cached results, after 10 minutes the cache is flushed and the build is retried, possibly failing again), so that's the very minimum possible.
If the failure was because you landed between the rsync of two files, then maybe things will heal right away and the 10m delay is enough. If the rsync times out or otherwise fails the upload, then it could indeed be days before that platform's package builds go through again and repair everything that's mismatched.