Answer: It sounds like winter dieback, although I'm not sure why that might happen. Thuja is quite cold tolerant. I wonder if your shrubs put on a lot of new growth late in the season and then did not have time to harden off before cold weather arrived? It's unusual, but it does happen. As long as the plants look otherwise healthy and the drainage is good, they should be able to overcome the problem. All you need to do is shear off the brown foliage to encourage healthy new growth. Best wishes with your shrubs.
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