Sometimes when I do a lot of multi-tasking, the app is killed by iOS. A possible flaw could be from the app itself, but the logic behind airplay also plays a key part.

I upgraded from SE2020 for the 5G connectivity. Afterwards I have been enjoying features like Magsafe / better camera which I did not care about. If you are still happy with the phone, just stay with it, but pretty sure you will have another level of satisfaction by the upgrade.