I don't know how exactly the arrowchat mechanics work, but when I enable caching (php APC) from vbulletin, arrowchat tends to disappear. Anyways, that's what I have noticed.
When I enable caching arrowchat comes and goes. If I disable caching, arrowchat stays and my cpu load triples. As one can see, caching is very handy, but arrowchat is too buggy with it.
Has anyone experience something similar to this? maybe we can find the root cause together.