Custom Column not getting added to questions

I've been able to custom columns in questions before where i add basic expressions like Convert Timezone or Date Time Diff.
However recently after creating a custom column, when i click on visualize, the custom column does not appear. Earlier i thought it would at least appear in the column section but is just not visible. However when i go back to the editor, the custom column vanishes too.

Troubleshooting info? Repro steps with the sample database?