BGA glue on some Motherboard models - TDR - National Repair Center
Some motherboard assembly lines like to add an extram stablization step to the BGA solder process by adding a BGA glue.
That glue disables successful reflows of any kind. The chip must be heated glue removed as well as washed in an ultrasonic machine under high temperatures to achieve a small success rate. The best option is to remove the chip and clean out the motherboard and Reball.