Using QGIS 3.6.2 I have a CSV file with a dimension string field. This table is joined to a Shapefile via 1 matching string field. I filter the table source using the Query Builder on the dimension field, e.g., "Code"='SE02'. The relationship is 1:many from the shapes to the CSV table source.
On opening the Attribute Table, i can see the filtered values associated with the shapes. If i change the filter, e.g., "Code"='SE03' I still see the values for SE02. I have tried opening the shape layer properties and clicking OK from the Join tab and nothing changes. I saw a few SE posts related to the Attribute Table not updating based on filter changes but not this symptom. I have seen it adjust if i move around the map a bit but the most reliable is to reopen the project.