Hi Daniel,
This appears to be a checkbox Content Control. It may have been set to not be deleted. This is in properties under the Developer Tab.
If you want, save a sample document with the problem on OneDrive or Dropbox and paste a link here. Remove any confidential or sensitive information first. I or someone else can take a look at it.
For OneDrive: See https://support.office.com/article/share-onedri...
For DropBox: See https://help.dropbox.com/files-folders/share/vi...
This forum is a user-to-user support forum. I am a fellow user.
I hope this information helps.
Please let me know if you have any more questions or require further help.
You can ask for more help by replying to this post (Reply button below).
Regards