For starts, the last stable BI version, at least for me, is 5.4.5.3. I know there is at least one more newer version marked 'stable', but I had issues in UI3 with that version and reverted back.
Almost every time someone has camera instability/loss of signal, it has turned out to be connectivity related and not cam related. As
@sebastiantombs stated, moisture can be an issue. I always use dielectric grease in all outdoor connections. Even taping the connection does not stop corrosion due to changes in humidity.
The next thing to check is the POE switch. Make sure you do not have it overloaded. When does this happen? At night? Are you using IR? Are other cams on that POE switch and using IR?