Voices questions on my iPhone 11 running IOS 14.01

iOS & iPadOS

Since iOS 13, I have selected certain voices to use in certain apps. For example Siri South-African female to speak in my newspaper apps. Siri US English female in Mail, Messages and Notes. Tessa in Facebook. On my language rotor I selected Aaron (Siri US English mail. Catherine (Siri Australian female. Everything works perfectly, except in Facebook. When I open FaceBook and swipe through the posts, it happens sometimes Aaron talks instead of Tessa.Is it a software bug or am I doing something wrong?