How to restore headphone jack after using lightning connector for audio?

Yesterday I plugged my Bose headphones into my iPad Pro’s (NPGJ2LL/A) lightning connector (using a 3.5mm - lightning adapter), because the adapter was already on the headphones (so I could use them with my iPhone) and I was curious to see if they’d work that way. They work fine. Today, however, I removed the adapter and plugged the headphones into the headphone jack and nothing comes out. Audio comes out the iPad speaker. They still work through the lightning connector, though, with the adapter. How can I restore the headphone jack functionality?