iTunes sync iPhone

I have a late 2012 iMac running Mojave, and using iTunes 12.9.5.5.

I plug my phone into the USB on my computer every night when I go to bed.

Always wait for the chime and verify that it is connected. In the morning, I always get that the iPhone could not be synced because it was reset. I then unplug the USB from the phone, wait a second, then reconnect and the sync process proceeds perfectly.

After more than a week of this routine, I gave something else a try.

When I connect my phone at bedtime, now I wake up the computer before connecting and everything works fine.

So it appears that connecting the iPhone to a sleeping computer is the problem. Why?