Hi Mark, I have this problem too! I read the log of Evernote workflow and find a way to fix it:
You can see the log of a workflow by click the bug icon in the top right corner of that workflow.
I find when I append a text, there is a error
"ERROR: Evernote[Run Script] 0:61: execution error: Can’t get application id "com.runningwithcrayons.Alfred-3". (-1728)"
When you click the [Run Script], you will find this is the problem from script "en_append.scpt"
So I decided to change the script.
Download Script Debugger.
Open folder of Evernote workflow(right click the workflow in the alfred workflow panel and click open in finder).
copy en_append.scpt file to another folder such as Document folder(Script Debugger can't find files in users/library)
Use Script Debugger to open this script file.
application id "com.runningwithcrayons.Alfred-3
application id "com.runningwithcrayons.Alfred
Copy the compiled script to its original folder.
Then you can append now!
I don't know if my compiled file is okay to run in your mac and I can't summit attachment in reply, if you want, you can send a email to me and I can send my compiled file to you.