plexus-interactivity was retired for F35 but was just readded last week. A very old (.eln109 !!) ELN build that had been blocked by the retirement was suddenly re-exposed, and (for obvious reasons) not being signed with the latest key, caused this compose to fail.

Generally, whenever the ELN dist-tag is bumped, I untag all builds from packages which have since been dropped from ELN+Extras to avoid situations like this. Doing so allows them to be cleanly and automatically rebuilt if/when they end up back in the composes. However, in this case, the ancient build, which predates my involvement in ELN, was blocked and hence hidden from my queries, so I missed it.

I untagged the ancient ELN builds of the package, and the next compose attempt succeeded. I'll also investigate any other blocked builds and handle them as well.