Smart Proxy won't sync

Cannot sync my external proxy. It fails with:

Parsing interrupted: The repository metadata being synced into Pulp is erroneous in a way that makes it ambiguous (duplicate NEVRAs), and therefore we do not allow it to be synced in ‘mirror_complete’ mode. Please choose a sync policy which does not mirror repository metadata.

Please read Error message (or warning) about ambiguous metadata during sync · Issue #2402 · pulp/pulp_rpm · GitHub for more details.

Expected outcome:
Until recently the sync worked. I have not upgraded or patched the system.

Foreman and Proxy versions:

Foreman and Proxy plugin versions:
Red Hat Satellite (build:
Capsule 2.5.21

Distribution and version:
Red Hat Enterprise Linux Server release 7.9 (Maipo)

Other relevant data:
The only related change I can see was that a colleague created a new version of an exisiting content-view.
We have a lot of CVs, CCVs, and approx 3000 clients.