The problem is resolved, though not satisfactory.
It appears the recent exim upgrade in combination with the tweak setting preventing the user nobody from sending mail to remote addresses is the culprit.
Although your PHP scripts may be setting the FROM: address, the system thinks that it is the user nobody and thereby dismissing the emails. This slao seems to impact any forwarders that go to remote addresses.
If you remove the checkmark on that tweak setting (as thephantom was alluding to), it should allow things to work as normal. Of course this is more of a band-aid as that tweak settings should not be having this type of effect, especially not on the forwarders.
And of course, as hostCP3 commented, always check to see if the symbolic link is still there. If it's not there, and you are trapping errors in your PHP email scripts, you would have been able to isolate that problem as the error would have been trapped regarding send mail not being found, however, the 'nobody' problem I am referring to, will not return an error in your script, which is what made it difficult to determine.