When choosing to have iOS "Speak" aloud a large portion of selected text, only the first part or a random part is read

Feature: After a user selects a large section of text, they are presented with a context menu (usually horizontal). When the user selects “Speak” from the menu, the text is then read aloud by the iOS spoken-text accessibility feature.

Issue: Currently, when a longer section of text is selected, and when “Speak” is selected from the context menu, iOS only reads a portion of the text. It either stops mid-way or skips to a different portion of the selected text and reads it.

Currently, this is reproducible on the iPhone 12 Pro, using iOS 15.2.1.

I was unable to determine what was causing the malfunction. This issue does not appear to happen within any other apps within iOS.