I think it may takes a few minutes for the system to shut down,especially if you are close to the Amp Rating, like by 0.1 or 0.2 A. In any case it is easy enough to see how many Amps your vest is drawing with a good Voltmeter. If you are within the specs you are OK , but I have seen 8 Amps quoted somewhere on a quick seach ,and above 4 Amps is quoted.
Quite a few factors involved here, even the state of charge of your battery may affect everything.Apparently that Canbus is very smart......
Don't you have the specs for that vest, as in a tag on it somewhere with the Watt rating?
Most vests seem to be around 60-65 watts, divided by 12 V= 5.4 Amps, That is enough to trip the Canbus if it is rated at 4 Amps, but you are good to go if it is rated at 8 amps.
I misprinted my earlier post, it is Watts divided by Volts= Amps, I'll try to edit before I get slammed......!
My bike does not have Canbus, but I added another accessory outlet to it with BIG wires direct to the battery,I did not like the size of the wiring on the factory outlet, now I can plug a charger right in it , and push or draw plenty of Amps.
BMW has an habit of changing things around without saying much about it, and often it is production date specific and even country specific so.......but I'll look around tonight and see if I can dig something out, in the meantime someone else may pipe in with the answer!