You can disable this option in Settings:
> Settings > Message view > scroll to section "Navigation" > uncheck "Show positions"
However, this option could be useful when "Conversation view" and "Swiping" are enabled:
It's to inform the reader where he is within the conversation and prevent swiping out accidentally, not blocking the reader from swiping "out", but it's helpful to know when the edges of a conversation (start /end) has been reached.