Not sure if this is something that is controlled by your plugin or by BuddyBoss (BuddyPress), but is there a way to increase the topic length when it is sent by email? By default (at least on my site), it is relatively short, so it makes it hard to reply by email because the entire topic is not shown, it is truncated.
Have a suggestions? Or is this outside of your plugins?
It sounds like you have the [topic-excerpt] tag configured in your bbPress Notify (No-Spam) settings. Try replacing it with the [topic-content] tag instead.
You’ll find the settings under WP Admin > bbPress Notify (No-Spam) > Settings > Topic tab.