The pachysandra on one side of my front yard died gradually in the past two years, but the other side (last photo) is OK. I have an irrigation system, and water everywhere regularly. I live in Long Island, NY. I'm not sure about the reason, may be fungus. I'd like to know the cause and how to fix it. Thank you very much.

I also checked a few landscapers, but they are not sure about the reason, either. They suggest I try this, try that, and something else if doe not work. They seem to be lack of the knowledge. Is the any company specialized in the plant diagnosis? Thank you.

Good side without problem.