We got the hosting provider involved to research the permissions and did a number of tests to recreate the error. Here's the feedback:
"It looks like when you initially save the edit, it appends .human to the end of the cache file (fd16406b64f1dca758f3526d25eebc9e becomes fd16406b64f1dca758f3526d25eebc9e.human). That works successfully the first time. The next time you save the edit, it searches for the file but without the .human at the end of the filename, which is why it throws that warning. It does save the edits that you make, but it is not able to modify the cache filename for an unknown reason. I would take this to the plugin developer(s) to see if they can further troubleshoot this issue. The file it references in the warning message is encoded with IonCube Loader, which makes it difficult for us to troubleshoot this further."
The cache folder has the proper write (delete) permission so that's working. It is just this warning message keeps popping up. I can anticipate someone making an edit, saving it and then reading it and discovering "oops, made a typo", goes back into the correct and when saving a second time is presented with this warning and will be concerned that the system isn't working.
Can you please assist in providing some technical information or guidance as to how we can fix this and stop this warning message. Our hosting provider did as much as they could but it would appear we need your team to be involved because of the encoding with ionCube.
Thanks for your help.