Uconnect is not developed by Apple, so asking Apple "what's up," is not going to help you much.
However you're not alone here. Numerous Jeep and Chrysler owners with Uconnect 8.4 systems (especially the 2013–2015 models) run into this exact issue after upgrading past the iPhone X. The Uconnect software just isn’t updated to handle the newer iOS Bluetooth profiles or authentication layers properly. Apple’s iPhones evolved, but Uconnect stayed stuck in 2015. The iPhone will often pair initially but fail to reconnect later, drop calls, or simply not show up at all as an audio source.
Since FCA (now Stellantis) hasn’t pushed updates for older Uconnect head units in years, your workaround — using a Bluetooth-to-aux dongle — is unfortunately one of the only functional options left ... and, it is pretty much "hit and miss."
If your Uconnect version is still on 14.x or earlier, it’s unlikely anything short of swapping the head unit (or adding something like a Crux or iSimple integration module) will restore full functionality. If hands-free calling isn't critical and you're just doing audio streaming, you're already doing what many Jeep owners have resorted to.