Things are just a little unusual.
The loon was off the nest again, as you have seen, and just returned now.
While it was off, it went out to meet a loon who was swimming toward the nest. But it was not the mate, and as she pursued the other loon quickly paddled with its wings and went out into the middle of the lake. So obviously it was another loon.
"Our" loon swam back to the nest but was in no hurry to get back up on the nest.
Then another loon came FLYING in and landed nearby.
The loon by the nest swam out to meet it and they swam together nearby. No hurry to back to the nest.
Just very unusual behavior all the way around this year.