On our partner community the users are not able to see the related to and assigned to fields.
Following below articles I changed org-wide sharing to private for all objects that could be linked to a task to private or disabled "track activities" on the object.
Relationship Fields not Accessible on reports for Partner Community User
This did not change anything. Fields are still not visible.
FYI: I also checked FLS and the report type: fields are visible AND added to the layout.
Any of you have something I could try?