Custom Dimensions fields not visible in tag setup

When adding/editing a Matomo Analytics tag (tracking type: event) the Custom Dimension fields are not visible for some reason. See the attached screenshot. The red line is where the Custom Dimension fields should be shown.

Other Matomo’s we manage contain the subheading “custom dimensions” to push custom dimension values together with an event or pageview, but in this instance those fields are simply not visible. Does anybody have an idea why this might be the case?

Some useful context:

  • We’re using an on-premise Matomo (5.1.2)
  • The Custom Dimensions module has been enabled
  • We have added a custom dimension of the type “Action” (via “setup” > “measureables” > “custom dimensions”
  • Browser cache cleared
  • The log viewer does not seem to contain any issues related to this
  • System check shows “CustomDimensions” is activated
    Thanks in advance for any help.