I have followed the instructions for w3 cache and now it’s at least giving me something in the source code, where it wasn’t before.
<!– mfunc a4f23670e1833f3fdb077ca70bbd5d66 –>echo adrotate_group(6, 0, 0, 0);<!– /mfunc a4f23670e1833f3fdb077ca70bbd5d66 –>
On the front end of the site, we just see: echo adrotate_group(6, 0, 0, 0);
I even tried disabling w3 cache and all other plugins, but still get the same thing.