Both my opponent and I had authority of the consuls (AOTC) out.

My opponent had fiendish panda on the battlefield. My opponent cast a creature, and I gained life, and then their panda received a +1/+1 counter. This happened multiple times. Their panda would gain +1/+1 counters when they gained life from their AOTC, and when I gained life from my AOTC.