Hey Max,
First of all, can we quickly confirm you are on 6.5 or later? If you are on an earlier version, it might be worth upgrading, since S3 pipelines have been significantly improved since then. If you can’t upgrade, you might have to bump pipelines_extractor_get_offsets_timeout_ms, but in 6.5 or later, this should not be necessary.
Otherwise, it could be a bonified a connectivity issue. Make sure the Master Aggregator can connect to your ceph node.