guest was dissapear but registered user still

[geevest.com]

For example,
in my forum there is currently active users : 800 ( 300 members and 500 guest)
and some times,after i do a refresh my site, iam not sure for the
time, teh guest visitors go down as drastic
become 202 ( 200 members and 2 guest) ( the numbers of the guest is
not always 1 or 2, but under 10).
but it will increase again as slowly..the number will go up again for
slowly like this 300 ( 260 members and 40 guest),
360 ( 300 members and 60 guest), slowly but it will up again as soon,
more and more..
but why just only for the guest that have to go down until that far?so
drastic numbers, but the members doesnt
change that much?
is this because of myn hosting mistake or there is something wrong
with my setting?

*i hope its my last question in my error.