Hello RoboSheila,
While there is no supported way to go back to an older iOS, this should be an issue that can be resolved.
Does this happen on all texts in all locations? The reason we ask is that Siri depends on being able to connect to servers in order to be able to read messages. If you are in a location where service is not available, then Siri would not be able to respond.
Just to confirm, does the same thing happen when not connected to CarPlay, or does Siri seem to be able to read messages as expected. Again, keep in mind the location of the device when performing these test.
It would be interesting to know if a text that Siri has trouble to read over CarPlay, is able to be read when CarPlay is disconnected, in the same location.
Have a great day.