These are the hacks I've got installed:
Number of Threads in User Profile
Show An Avatar On Who's Online
Mood Hack 3.5
bbSpoiler
Timezone Image In Profile
Members Who Have Posted Today
Who Has Read A Thread
Borgs BBCode Pack
Forum Skin In Profile
Join Days
Simple Breadcrumb Below Last Post
Separate Sticky & Normal Threads
Members Who Have Visited Today
Most Ever Visitors, Posters, Chatters
I've gone through the code of each and none of them make any reference to the maxloggedin datastore (except of course for "most ever visitors, posters, chatters").
I am also running vbAdvanced CMPS which
does have a "who's online" module which makes references to maxloggedin. Do you think it could be the culprit? Thanks.