Okay - though much trial and error I have found a potential solution to this problem. I don't know if it's just going to swap one problem for another or if this represents a bug in Lucee 4.x or what.
In all of the Lucee 4.x downloads that I can find (and on my machine) both of these files exist:
/express/lib/ext/apache-commons-httpclient.jar
/express/lib/ext/apache-jakarta-commons-httpclient.jar
On a hunch that they were in conflict, I removed "apache-commons-httpclient.jar" from the folder and my problem vanished. Suddenly my CFHTTP calls started working again.
Perhaps these have always been present in the directory but something recently changed on MacOS to trigger the condition?
Is anyone else running 4.x who can confirm this or maybe someone with more knowledge about what these libraries do can help fill in the blanks with more information?
Removing that file definitely makes my test case work. I haven't spend a lot of time to look for other side effects yet.
-Cameron