I opened a question on Exchange 2016 Public folder shared contacts not working in OWA 2016, but working fine with the full Outlook 2016 client. That question went nowhere. However, someone suggested I look for "duplicate LegacyExchangeDNs" as a possible cause.
I have ran a report looking at LegacyExchangeDNs. I need help interpreted the report. I didn't see duplicates, but I do see very different entries. Exchange 2016 works flawlessly except for the public folder shared contacts which don't work at all. The sample ExchangeLegacyDN report is attached.