Fill and Sign is not available due to the document's security settings.

I've created forms some forms with e-signature fields enabled and the security settings are set to

Filling of form fields = Allow

Signing = Allow

When clients come to use the forms, they are able to fill them in but can't sign and receive the error message "Fill and Sign is not available due to the document's security settings."

Also on mobile (android), the signature field is completely removed. 

The client is using Adobe Acrobat to fill and sign forms. 

I've been creating forms the same way for a while now and this problem has only just cropped up. The client said they have no problems with docs that don't have any security at all but I would like to some to protect the content.