Alaskan cedar trees are important in Alaska and British Columbia where there is usually much moisture.  Perhaps, therefore your tree is reacting to the lack of moisture and hot weather.  You therefore might need to keep the soil moist.  See https://pnwhandbooks.org/plantdisease/host-disease/cedarspp-cedar-flagging.  The Morton Arboretum website, mortonarb.org, also indicates that the plant needs consistently moist soil.
You should call a certified arborist if you suspect diseases or insect infestations because I cannot help you through pictures.  You can find a certified arborist in your area by searching treesaregood.org.  I hope you can solve your problem.