We are the editors of SvnGateway.
I just see now your question, 2 years later ... I didn't know this site even existed, and we get no notification. Answering it now if someone else ever visited this question again.
The SvnActivity is a button that launches a new screen in Jira UI which shows you the activity. For some reason, Jira UI shows a weird gray rectangle that is confusing indeed.
Yves for Matrix Requirements support