I didn't want to post this right away, but since nobody else posted about it, I guess I'll be the one. Several of my riding pals have a glitch when I visit their farms. I am able to help them more than five times. The 'energy' bar keeps refilling the more I collect, so I'm able to go around and clear their entire properties. Then I don't get any rewards for visiting, as I never use up all of the energy. This happens on most of my neighbours (I don't keep track of which ones!), and has been happening daily for approx. four days now.
As nice as it is to boost up friend levels so quickly, I want IOU's again!
I've had it happen a few times, and it seems to be related to friends that you've chosen to Cheer for you in an event.
Thanks for letting us know. The team will check into this to see what's up!