iPhone Bluetooth Disconnecting in Toyota

Hello Everyone. Since the my wife updated her iPhone to iOS 15 and higher, my wife is having constant problems with her iPhone disconnecting in her car - which is a 2015 Toyota Avalon. Most of the time it just looses the Bluetooth connection but the call is still connected on the phone, and other times it will also hang up the call. The only way to reconnect the devices is to turn the car off, and back on. We have updated the firmware in the car to the latest version. The problems did not start occurring until her phone was upgraded to iOS 15. We have cleared the Bluetooth connection in the car and phone, and re-paired them and that has not helped. Is anyone else having problems with iPhones and Toyota vehicles? Thanks Everyone. Greg