It could be a problem in PowePress, during the validating process. The media file is tested to obtain the duration and file size. If you do not mind, please try saving the m4a episode specifying the file size and duration and see if you still get the memory allocation error. That will narrow the problem down to the validating logic if saving when you specify the duration and file size does not give the memory error.
Also, I will take a quick look at the Duplicator plugin. Plugins in the past have changed the memory limit for PHP scripts, which is a bad practice but would obviously cause the issue.