I took my X3 to the garage that fitted the performance chip two years ago, wanting to check that out before going to the BMW dealer. They've disconnected the chip and asked me to drive the car for a week and let them know if this resolves the problem. If yes, then they will reset the chip parameters. If no, then they will look further or send me to BMW.
The drop in power / acceleration was quite noticeable on the drive home ie you forget what kind of boost you get from a chip remap.