Provided the bridge mount and screws were epoxy glued, as I do with every scope mounting I perform, the single rear screw should be fine. I have a Weaver bridge mount fitted on my Mauser 404 from the front receiver ring (2 screws) to the rear of the safari sight (one small screw), all epoxied glued and this set up hasn't moved in decades of shooting the rifle. Only has a 2x20 Leupold EER scope mounted but a low power lightweight scope is all you would need mounted in the normal position on a 404 rifle anyway.
Mounting a big heavy scope on any rifle that recoils heavily is asking for trouble with both scope and mounting system.