Shifting bridge and nut
Instruments- discuss specific features, luthiers, instrument problems & questions
First try changing the string slot or possibly the anchor point. The last thing is a single spot of glue to anchor them [may need to be replaced in the future]. A thin piece of paper/foil behind the bridge [anchor side of bridge] may tighten the slot enough to prevent the bridge from sliding.
If you retuned from DAdd, you may need to install a melody string the same size as the middle string. The melody string used for DAdd is usually smaller/lighter gauge than the middle so when it's loosened to A the tension goes down.