I'll give this a go when I get home Ken, and report back on my findings.Have you removed ("Forget This Device") the D500 in BT Settings? Try that prior to trying to re-pair the phone after the update.
If that doesn't help, try this: remove any connections with the D500 in BT settings, then go to SETTINGS -> GENERAL -> RESET and Tap the RESET NETWORK SETTINGS and do a reset. Your phone will do a restart on its own. I have used this several times in the past to resolve both BT, cell, and Wifi connection issues and each time it has been quite successful. FWIW - this is also step 1 if you call AppleCare with a networking or BT linking problem, so ....
NOTE: Don't tap the other resets as you may end up with a "new" phone as they can clear everything on your phone!! There will be dire warnings that popup!! If you're just resetting the network, just say OK!!
NOTE 2: After reseting your network settings, you will need to rejoin your wifi network, so make sure you have your password handy. It also resets your phone's name to "iPhone" so if you have a specific name already, as I do (Ken's iPhone XR) you'll need to re-enter that in the ABOUT section (helps me ID who's phone is connected in our car ... mine or my wife's!). Although the reset does clear wifi network info, it will not clear established BT connections. Problem BT connections must be removed manually ("Forget this device" in BT settings).