@Voice stops reading aloud, or pauses for several seconds then resumes, when screen is off

It’s not a “bug in @Voice”, but how your phone is slowing down apps to “save battery”. You need to adjust system settings to prevent this, nothing can be done in the app code for this.
 
Open Android system settings – Apps – press to show all apps – find and press the TTS engine app for the voice you are using. For example, if you are using Google voices, find on the list the app named “Speech Recognition and Synthesis from Google”. If you are using e.g. Vocalizer TTS voices, find and press “Vocalizer Voices” app instead etc.
 
Next find “App battery usage” and press it. Then change the choice from “Optimized” or “Restricted” to “Unrestricted”. Go back up 2 levels and double check the @Voice Aloud Reader app. It should also be set to “Unrestricted” battery use.