Well, start with the frost nade plugin, disable that and see if that works.
If that doesn't then i suggest removing plugins one by one and seeing if it solves it (or removing them all and installing them one by one)
I know this isn't exactly the best solution as you are running as server, but if you really want this thing stopped then I'm afraid you don't have many options.
Alternatively set up a dedicated server, set it up exactly like your server where the problem is happening, and do what i suggested above, so that you do not loose players because of the down time!
It could in fact be two different plugins that aren't compatible (or not fully) and having them both loaded at the same time is what is causing this.
I'm kinda new so i don't exactly know a whole lot but these are my solutions, trial and error is probably your best shot im afraid.