[Mariner]

Whatever/whomever it was, it was picked up by rudimentary PI radar.

If I was to guess, I’d guess China finding out if they could get away with it.

So much for Chinese stealth.

[larrytown]

The wings look like they're a bit longer on this new bird, and the TWO X-47B's have been sidelined/defunct for the last two or three years is latest public info is correct.

Some more digging, and here's our beastie - RQ-180. Very secretive US recon - here's a similar looking aerial shot to our Filipino bird:

[Tallguy]

21,000 ft and pulling a contrail like a B-17 operating over Germany in 1945... And reportedly ‘stealthy’? Doesn’t add up.

Could have been a systems problem, or maybe the UAV had been air tanking shortly before it was detected? Maybe the radar picked up the tanker before they broke off?