Since late last year (I forget exactly when), I've had a bizarre issue with my Lightning-3.5mm adapter (A1749, from Apple). When I plug it into my device (iPhone XS), and plug in a set of bog-standard wired EarPods w/ remote+mic, the device acts like I'm pressing the main button on the remote. It opens Siri, won't accept volume changes from the remote, and won't transmit audio from the microphone. I can listen to audio on the EarPods, but that's it - no volume control, no mic input.
I see the same behavior using the adapter on my iPad (6th generation) - immediate Siri prompt upon plugging in the 3.5mm side of the adapter. I can plug in the EarPods to the iPad's native 3.5mm jack and get the proper behavior. I've verified all of this with multiple pairs of EarPods.
This started happening on both my iPad and iPhone at roughly the same time, late last year (but I don't recall if it correlated with a specific iOS update). It feels like a software issue, but I have a hard time believing Apple would ship code that debilitates the adapter for this long.
The inside of the 3.5mm side of the adapter is clean, no conductive junk that I can see. I'm working on getting another adapter to test with. In the meantime, any thoughts?