Hello
I'm seeing a schema validation error from the presence of a my:o_count field in each of the my:task elements, between the my:t_name and my:t_code_name elements.
Looking at the form's MDS, it indeed does not have an o_count field in the task group (there is an org_count field, but that is something else).
I know you say you haven't modified the template recently, but the only thing I can imagine is that this field was somehow deleted.
In order to remedy this issue, I would suggest adding an o_count field to the MDS in the correct location. One other option would be to modify the XSLT to remove the part that creates the o_count element (you can find it by searching the XSLT file for o_count).