What temperature do you run your tank? How stable is your tank temperature? How much does your temperature fluctuate?
Last night, I lost a head on my NY Knicks with what looks like BJD, after losing a double head green torch a couple days earlier

The only thing I could think of that could have stressed the torches is my tank temperature getting a little too high or fluctuating too much, almost hitting 81 at its peak this week.
My tank temperate usually averaged at 77.5, this weeks slightly warmer weather and my non-functioning A/C meant a slightly warmer tank at 78.64 tank temperature with higher peaks than usual.
I'm not sure temperature fluctuations are the reason for the BJD in my case. The lost green torch could have set off a chain reaction, that maybe wasn't helped by the increase in tank temperature. This is my best guess so far, as nothing else in the tank has recently changed.
Would be interested in hearing about your tank temperature, maybe the two cases are correlated.