https://github.com/NodeBB/NodeBB/commit/a7bb5893e8297853cad15d104c87ad72d5ec0db2 might fix this issue, the same was happening on topics as well. If you navigated from topic to topic or from category to category, the socket listeners werent removed.
barisusakli committed to NodeBB/NodeBB
fix dupe event listeners on category
only happens if you navigate from category to category
I'm running 0.5.3 stable. Ok I will try tonight when I'll be at home.
Edit: @julian I tried to disable plugins, it's still doing the same thing unfortunately. The quick solution that I've found for the moment is to deactivate the upload of a thumbnail for topics.