This happened to my daughter IN the EU on a BA and IB flight. Trying to file for EU261 compensation through 2 different agencies; one agent said the reply from BA was due to "weather" while a second agent said the reply from Iberia was "unusual air traffic at LIS and therefore, cannot be compensated". This, despite the fact my daughter and all other passengers were told, at the time, it was MX issues. EU261 covers neither weather or ground control probelms.

She pursued it and pursued it and pursued it, and eventually BA awarded her 13,500 miles. So you might want to try asking for miles.