Changes made by JMWE post-functions are not always visible just after the post-function execution. This is because JMWE post-functions (as any other post-functions implemented by JIRA Cloud add-ons) are processed asynchronously, after the transition completes. This helps ensure the stability and performance of your JIRA instance.
This problem is tracked by Atlassian at: https://ecosystem.atlassian.net/browse/ACJIRA-1098
You can either manually refresh the page to see the changes done by the post-function, or enable the "Auto-refresh issues" option in the Configuration page. This option is enabled by default.