Is there an agriculture department at a local university that might be able to help with the diagnosis of the problem? If you can identify it with certainty, it will be relatively easy to follow-up with the appropriate fungicides.
I’d also be curious if fungus on junipers is a relatively common phenomenon where you live. If so, that might be a clue. Are there any nearby nurseries that can help?
I can’t identify the problem well from photos, but it’s clear the tree is stressed. I had similar damage on some itoigawa and simply watering less frequently coupled with good weather and mild fertilizer cleared up the problem.
When you repotted, did you leave some old soil in the middle of the rootball? If so, it might be worth repotting again this year or next to get rid of the last of the old soil. Even a little bad soil can cause surprising stress to junipers in some cases.
If the soil and watering is perfect, that leaves fungus as the next thing to address. The treatment you mentioned sounds relatively accurate, though the specifics are noted on the labels of the products and only apply when you know what problem you’re trying to solve. In general, when it’s warm and humid, fungus can spread rapidly.