<field name="my_many2many" context="{'tree_view_ref' : 'my_module.my_model_tree_view'}" />

but where you define the view 'my_model_tree_view' ..make priority same as the default view for the many2many or many2one model <field eval="7" name="priority"/>

Some little tips :

1. Did you check which view is called from the action?
2. Maybe the form view called is not the correct one (check priority)
3. In the web UI, update your module

Hope it can help

It should work for at least one2many fields since it is also used in the stock.picking object in file stock/stock_view.xml:

<field name="move_lines" context="{'address_in_id': partner_id, 'form_view_ref':'view_move_picking_form', 'tree_view_ref':'view_move_picking_tree', 'picking_type': 'internal'}"/>

You can try to remove the my_module. before the name for the view.