Unfortunately, from my cynical POV, there are a lot of POS's that have no problem taking crabs out of traps. Often it is these huge boats that will pull them and then just move on. Usually they even leave your gate open or dump the bait out as well. In the Seattle area, a friend says he has watched a certain group of people just go from one pot to another pulling crabs out. When questioned, they suddenly speaky no english....
You can zip tie your pot shut and would know if it was messed with, unless they were taken out through the gate.
Not sure it is a bait issue as I used bait for two days, pulled it out, stuck it in the freezer and used it for another two days catching crab the whole time. If you can, you should hang your bait from the top of the pot as some areas have huge numbers of the little crawly shrimp type things that will eat all of your bait if given the chance. I've caught crab with freezer burnt goose legs as well as other freezer burnt stuff. Fresh is probably better though
Light should not be an issue in 50+ feet of water.
Another thing folks here will do is set their pots at low tide with a lot of weight and just enough rope to reach the surface. When the tide comes up, noone can see the buoy to pull it, then they pull it the next day at low tide.
Sometimes it does seem a mystery why there are no crab in the same spot where you got a bunch the previous day.