It sounds to me like you had a bacterial conversion of CYA into ammonia when the bromine level went to zero. Did you notice the CYA level drop from before you left until after you came back and noticed the zero bromine level? That can create a huge oxidizer demand. For every 10 ppm CYA drop, it creates a nearly 30 ppm FC chlorine demand. The following is what you added in FC for a 30,000 gallon pool:

12 pounds of Burn-out 35 (Lithium Hypochlorite with 35% Available Chlorine): 17 ppm FC
24 pounds of Burn-out 3 (57.8% Cal-Hypo): 55 ppm FC
64 pound of Burn-out (you didn't say which type was used -- I'll assume it was 35 so lithium hypochlorite): 89 ppm FC
40 gallons of 12.5% chlorinating liquid: 160 ppm FC
20 gallons of 12.5% chlorinating liquid: 80 ppm FC

So that is a total cumulative demand of around 400 ppm FC. Such a demand can come from bacterial conversion of 133 ppm CYA into ammonia. Was your CYA high before you left? You said it was 35 ppm, but how did you know it's level? If you used Dichlor to activate your bromine then the CYA level can get very high because for every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.

See Degradation of Cyanuric Acid (CYA) for technical details and It Can Happen to Anyone - Zero Chlorine, CYA-->Ammonia for my personal experience with this phenomenon. Did anyone bother to do an ammonia test? If your bromine level is still zero, you can get an inexpensive ammonia test kit from a fish/aquarium/pet store since that would help to confirm the problem and also give you an idea of how much more oxidizer you are going to need, though a properly-done demand test would tell you that (it sounds like they didn't do their demand tests properly).

I also assume they aren't doing something stupid like raising the bromine level so high as to bleach out their DPD tests and then thinking that there isn't any bromine in the pool when there is actually too much bromine in the pool. Do you have an OTO chlorine/bromine test you can use for confirmation?