Workflow Studio - Can't move all catalog variables from available to selected column

I have a large catalog item which contains a lot of variables.

When using the Create Catalog Task action, the issue is that when I move all the variables from the available column over to the selected column many do not move. 

Weirdly, I see all variables at the RITM level but only half of them move over to the SCTASK.

I tried increasing the task_variables max length but it did not resolve the issue.