When you rentals are cancelled at the very end of the season, not only do you get less rewards chest. You also get way less chance on Chaos Legion packs! On silver III your chance is as low as 0.25%!
I know a lot of people rent out there monsters and cancel it at the end of the season to boost their own CP.
There is nothing we can do about it, There is no way to see difference between reliable lenders and lenders who cancel at the end of the season.
The cancel period is nice, but renting soooo much more expensive on the last day of the season it cost you almost triple!