I haven't had this before, but it may be that your phone just can't decode more than one video at the same time. The way this is implemented is to decode the video stream twice: once for rendering, and once more for muxing it into an mpg file.
Its not that TelloFpv doesn't run on Android 8. This app is working for a few thousand users now with different phones from Android 5 to Android 9. Its also not a problem that the phone isn't powerful enough, it certainly is. Is more likely that something is just messed up in the codec of your particular phone.
You may try to reboot, wipe the dalvik cache, restore to factory defaults, go back to the previous ROM, etc.
If you are on the full version, I can offer you a refund. In that case send me the GPA number of the purchase (see mail received upon purchase ) to
[email protected]
Other than that I can't help, sorry.