Wrote into customer care with the following last month:
I believe I am due compensation under EU 261 for a delay of over three hours in reaching my final destination (ORD) from VCE on 2017-07-06. UA169 was delayed due to mechanical problems, resulting in a 3.5 hour delay in reaching my final destination (9:43PM actual vs 6:10PM scheduled). I believe I am due 300 euro compensation under EU 261 for a flight out of the EU of more than 3,500 km that led to me arriving at my destination more than 3 hours but less than 4 hours after I was scheduled to arrive.
Just got the following response (nearly a month later):
We sincerely apologize for the inconvenience you experienced when your recent flight from Venice was delayed and you missed your connecting flight.
Prior to departure, an unexpected safety shortcoming beyond our control impacted the operation of the aircraft originally scheduled for your flight. I regret it took so long to resolve the issue and get you on your way. Although schedule reliability is a primary goal, we know you understand that the safety of our passengers and crew is our first priority.
Although cash compensation under Regulation EC261/2004 is not applicable in this case, we certainly recognize that your travel plans were adversely affected. In appreciation for your patience during this extraordinary delay, I have requested an additional deposit of bonus miles to your MileagePlus account. Please allow up to 3 days for processing.
We appreciate your business and loyalty as a Premier Gold MileagePlus member and look forward to welcoming you on board a future United flight.
They've deposited 3,500 miles.