Please check the notes.ini of the server: There you will find entries for ServerTasksAtX. X stands for the hour, when these tasks start.
Let the server show all ow them by typing: show config ServerTasksAt*
Usually there is a line:
ServerTasksAt1=Updall
If the server starts this task an another time, then this must have been changed, or the timezone of your server is not correct.
Also search for program documents in the nab, that have "updall" as task, but as you stated there are only fixup and compact tasks.
Be aware: If you start a compact with option -D this will discard all indices, so that after completion they have to be rebuild.