"Error fetching diverging counts for branches" seen loading branch page

On https://gitlab.com/gitlab-com/runbooks/-/branches using a canary host, I'm seeing:

The counts appear to be there. However, the browser just returned a 304 Not Modified:

https://gitlab.com/gitlab-com/runbooks/-/branches/diverging_commit_counts?format=json&names[]=master&names[]=gitlab%2Fmichalw%2Fget-redis-commands-from-tcpdump&names[]=devin%2Fpostgres_troubleshooting&names[]=add_chef_groups_docs&names[]=T4cC0re-master-patch-19837&names[]=add_azure_testsub_notes&names[]=revert-555f6ca6&names[]=walg-wale-rules&names[]=T4cC0re-patch-1&names[]=jts%2Fdont-wake-me seems to return the right values too.

This seems like a frontend bug not gracefully handling the 304 message.