Pull request workflows have suddenly stopped working

I’m using a monorepo structure, with a number of separate projects in either the packages or services directories.

I’ve got a number of different workflows set up to test the various projects. These are triggered on pull_request with path filters. This has worked perfectly up until the last couple of weeks, where some workflows just won’t trigger.

The following workflow triggers fine:

name: 'Testing - Packages'

on:
  pull_request:
    paths:
      - 'packages/**'
      - '!packages/cloudformation/*'

jobs:
  test:

However the following just won’t run unless I removed the paths filters:

name: 'Testing - Forms API'

on:
  pull_request:
    paths:
      - 'services/forms/**'
      - '!services/forms/cloudformation/*'

jobs:
  test:

There are changes in the pull request for files under the packages and services/forms directories, so they should definitely both trigger. As mentioned above, the forms workflow works if the paths filter is removed.

All the workflows are enabled.

Has anyone else experienced issues like this? Am I missing something obvious here?