I'm also on Android with the Plus subscription and I also get this. It usually reconnects by itself a few seconds later, but if it doesn't, I've found that you can get to the answer by closing the app and reopening it.
I had the same problem and I figured out how to fix it! For Samsungs, Apps ‐> ChatGPT -> Battery -> Unrestricted completely fixed the issue for me, it continues thinking/outputting in the background now. Should be a similiar setting for other Android distributions. Basically, it wasn't the app's fault, the OS is just halting it in the background to save battery.
Thank you! That fixed it for me on Pixel 8 as well. Would be great if the app suggested this as a fix.