The Account Site issue turned out to be a visibility permission problem (someone had switched it off in SF). Switching on visibility sorted that issue.
I’m still having problems with the Contact record sync. To resolve the AnnualRevenue problem on the contact record sycn turned out to be a problem with the SF Lead record with that field having it’s visibility switched off. Switching that on cleared the sync mapping errors. However, I now find that all the Status columns are green on the Contact field mapping, and yet still the main checkbox on the Contacts for ‘enable sync’ remains disabled and I don’t know why.