Yes, it is probably not the support system since the feeders were sharp. Do you have the photo that you can send to me? You can email to email@example.com
. I can take a look.
If you think you need sturdier support though, I would recommend a Wimberley WH-200 full gimbal. You will love it. This makes birds in flight a breeze. Of course the trade off is that it's pretty bulky and 4.5 lbs. If you don't care for a gimbal, then a RRS BH-55 is also a gem. It's a ball head that is built wonderfully and holds substantial weight: 50+ lbs. You might want a Wimberley sidekick for this setup, if you want to track birds in flight (BIF).
hmm...if most of your shots were at 1/800 to 1/1250 s, then I'd suspect a back focusing issue. Do this, take a page from a book and place it at a 45 degree angle on a table. Then with the 500mm on a tripod at the same height as the book, move it to the minimum focus distance away from the book. Then focus on a particular line in the book and judge if the AF is back or front focusing. If it is, then play with the micro auto focus adjustments in increments of +/- 5. Then once you are getting close, move +/- 1 increments.