Yeah, these are a result of running the imagebuilder during a package upgrade, either the package or its index has completed uploading, but the other one hasn't. Then, when ASU fires off the build, opkg sees things in an inconsistent state with the above errors as a result.
As you've found (at least @hrw), waiting a bit for the package builds to finish and retrying is the current solution.
You will also see this occasionally from just a command line opkg update && opkg install something, it's not something ASU is doing. The situation is caused by the frequent rolling package builds.
Just for background, the package build deploys a lot of stuff, for example in https://downloads.openwrt.org/releases/24.10.3/packages/aarch64_cortex-a53/packages/ we've got 4574 files using 2231 MB. (The magic all happens in https://github.com/openwrt/buildbot if some devops wizard wants to take a look and see if they can come up with some ideas.)