You might consider posting on the "container gardening" forum, because there are issues unique to growing in containers, as opposed to growing plants, trees, & shrubs in the ground. I grow blueberries, but mine are all planted in the yard, and I have never seen the symptoms you describe. Be sure that the container has a drain hole in the bottom, and the soil mixture, aka "growing medium," should be capable of allowing excess water to flow through, and out the bottom.

Heather,

From your description, you may have phomopsis twig blight. This disease has been vexing me, and my planting of 13 blueberries is now down to 7 survivors after 5 years. I am trying a program of fungicide spray this year. I feel like giving up on blueberries because of this disease. Interesting that I seem to be the only forum member with this problem.

Good luck,
Marc

I have the same issue and trying to figure out if it can be treated.