Step attach_workspace now just attaches files from 1 job only

Hello,
We have a build process that involves 4 parallel jobs that all feed into 1 job. The 4 parallel jobs are different automated test runners that all produce test coverage reports. The 1 job then uses attach_workspace to get access to that output and collates them together into a final coverage report. This setup has been working fine for about 2 years.
In a recent build, the output from 3 of the 4 test jobs stopped being delivered to the workspace. Now only 1 of the 4 is there. There’s nothing in the commit that changed anything about the CircleCI build. I’m really scratching my head about this. What might have caused 3 of the 4 test jobs to stop dumping their output in the workspace of the collate job?
Thanks

“Collate Coverage”:
<<: *env
docker:
- image: …
aws_auth:

steps:
- checkout
- prepare_directories
- attach_workspace:
at: /circleci/workspace
- run:
name: “Collate and check minimum coverage”
command: ruby ./config/ci/coverage.rb
- store_artifacts:
path: coverage/coverage.tar
- store_artifacts:
path: coverage/coverage.json