This is the line that is causing trouble: https://github.com/q2a/question2answer/blob/master/qa-include/qa-theme-base.php#L2104
That is the content of an answer being displayed by the base theme. That is certainly not a Q2A core issue. Most likely there is a plugin or custom theme that is messing with how answers are being displayed before that function gets called.
How to diagnose: Remove the first plugin directory under the qa-plugin directory. Check if it still happening. If it is, do the same with the following directory until you run out of them or find out it is not happening anymore. If after removing all plugins this still happens it is considerably likely that a custom theme is responsible. You can switch to the Candy theme and test if this still happens. If it is still happening then you have performed a core hack.
If it is a plugin or a theme issue, you should stop using it and contact the developer. If it is a core hack, then roll it back.