THREAD WARNING: Plugin should use a background thread

Hello,

I am getting the following warning starting from iPhone 5 and iOS 10.3.3:

**THREAD WARNING: ['TTS'] took '638.905029' ms. Plugin should use a background thread.**

It’s a real time App (a GPS) and I am using other plugins which are giving the same warnings and the App in iPhone 5 is really slow compared to an iPhone X. You might think this is normal of course because the iPhone X is much better, but the App is also working much faster on an Android 7 which isn’t much newer than iPhone 5.

How can I get rid of this and make the plugins run in background? Why am I not getting these warnings on Android or iPhone X?

Thanks!

No solution to this? I’ve seen a lot of topics about this but no one can solve it. How can it be possible?