After Catalina updated itself to 10.15.1 just yesterday, my iMac has slept through the night like a baby.... Hope it would be the same coming night.
Didn't worked next night. Still waking up more then once an hour. Looks like it works once after a proper reboot, but then gets into some state where it wakes up more then once an hour. I have an external Monitor which wakes up too and brightens the bedroom with "not connected" message. Also, I can hear annoyingly loud 3T fusion hard drive of iMac.
I will try to reboot tonight and see if it would help the problem. Will report here.
My iMac is configured to go to sleep at 10:00pm every day in Properties > Energy Saver > Schedule.
pmset -g log report, the first night (when it worked) it has the following message right before it goes to sleep:
2019-10-30 22:10:29 +1100 Sleep Entering Sleep state due to 'Idle Sleep': Using AC (Charge:0%) 29966 secs
And this is the same line for the next night where it didn't sleep through the entire night and were waking up periodically (It is configured to be allowed to sleep when the display is off, and the display goes off after 15 minutes idle.):
2019-10-31 22:10:29 +1100 Sleep Entering Sleep state due to 'Software Sleep pid=205': Using AC (Charge:0%) 1599 secs
Note that pid=205 is the
loginwindow process running in user space.
Note the sec value at the end of the log record. 29966 secs equates to 08:19:26, and 1599 secs is 00:26:39. So it makes sense. The second time it went for a shorter sleep despite my Schedule setting.
So it looks like between the fresh boot up state and the following (after wake up) state, there has some hand over of duties happened, and the other system failed to set up the sleep parameters the same way.
Note that on Energy Saver screen I have only 'Put hard disks to sleep when possible' checked, the other options like 'Enable Power Nap', 'Wake for network access' and 'Prevent computer from sleeping automatically when the display is off' are all OFF.