**UPDATE: This issue is resolved for me by manually installing the workflow from GitHub.
I'm also receiving the invalid argument error when adding a new task. When debugging, the message I receive is:
[2017-09-01 01:02:40][STDERR: input.scriptfilter] ./shell/todo.parse.sh: line 52: INBOX : command not found
./shell/todo.parse.sh: line 53: todoist_create_task: command not found
./shell/todo.parse.sh: line 54: : command not found
[2017-09-01 01:02:42][ERROR: action.script] module.js:491
throw err;
^
Error: Cannot find module '/Users/user1/Library/Application Support/Alfred 3/Alfred.alfredpreferences/workflows/user.workflow.2817A63C-F83B-4358-A9BE-C87B62C5393C/index.js'
at Function.Module._resolveFilename (module.js:489:15)
at Function.Module._load (module.js:439:25)
at Function.Module.runMain (module.js:609:10)
at startup (bootstrap_node.js:158:16)
at bootstrap_node.js:598:3