I have found out that description of Custom Field - single Checkbox is placed right next to name of the checkbox, see attachment (description-types.png and description-custom-field.png). I think that it is caused by the latest update to 3.3, because in i.e. Types 3.2.4 it is placed under the name (see description-types-324.png, but it is another site so the text is little bit different). If you will repair it, please consider making the name of checkbox to be bold like other field names (see the last attachment how it could look like).
I would like to inform you that we just released Types 3.3.1 which contains the fix for your issue. Please update Types plugin accordingly and try to resolve your issue.