Hi, and thanks for contacting us at OSU Extension.  You caught me walking out the door, so I am forwarding on your problem to my Wednesday plant clinic team and will follow up first thing Friday.

Thanks again for your question, we worked on trying to find solutions and found this previous response from a Minnesota Master Gardener re a similar situation at this link:
https://ask.extension.org/expert/questions/38206  However, we think that it may be not enough room for the plant to thrive.  Perhaps too much or too little water, but probably too small a space (the half wine-barrel), even if the plant is a dwarf.  Perhaps incorporating some compost or providing fertilizer, may help as well. 

I hope this helps you rectify your problem.  Let us know if it persists.

And, after a bit more thought, we realized that the cultivars you have in barrels (Is the honeycrisp in one too?) are not very resistant to a number of diseases, so that may be a future consideration for you. Here is a link to a chart that may assist you:
http://pnwhandbooks.org/plantdisease/cultivar-susceptibility-tables/apple-cultivar-susceptibility