I replaced the incoming mail servers yesterday and this resolved the issue of spam not being scored. For some individuals, even though spam is being scored correctly, it is not being placed in the spam folder. What those have in common so far is that they all use tcsh for their login shell.
I found that I had not installed tcsh on these servers so did that around noon today.
I found there were some other shells missing, basically everything except sh, bash, and dash, and installed those as well. If you get spam in your INBOX and it has a header that shows “X-Spam: Yes”, please do not delete it and contact support. Thank you.