[noblehops]

It looks to me like the pad delaminated and the friction material just fell off. This happened to me on one of my BMWs last year. As far as the uneven pad wear, there could be a few reasons for that, including dirty sticky pistons that need to be cleaned, dirty or grooved pad retaining pins, dirty dry caliper sliding pins, and possible a failure to recenter the caliper at the last service. Just reset on it all, remove the caliper, push the pistons out very carefully and clean them with a cloth shoestring, clean and inspect the pad retaining clips and replace any that are not round and un-notched, and clean out the sliding pin pockets and the pins themselves, and lubricate them with the appropriate high-temp brake grease. Finish with a fluid flush and bleed. Do both calipers. When it’s all back together, unweight the front end, give the front wheel a hard spin and clamp on the brake lever. Do that a few times to center things.