Answer: This could be due to winter damage with the effects only becoming apparent later on in the season when the plant is stressed by heat. Winter sun, either directly if the plant becomes dry or by reflecting off the building and interfering with dormancy, can damage stems and needles and bark; oscillating soil temperatures as happen with the relatively poorly insulated roots in a container can severely damage roots as well. In my experience evergreens do not overwinter easily in containers and most do show stress the following the summer, often they do not survive an entire year as a result.
Another possibility is that they are bothered my spruce mites which typically spread to damage an increasingly expanding section of the plant. You might consult with your local county extension to see if they can give you a specific diagnosis and based on knowing that, determine how to proceed.
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