Can't Connect to Network Volume on Startup

Greetings all! I've got a weird little issue trying to mount a volume at startup on a mid-2010 Mac mini I'm running headless as a Plex server.

I have all of my video content stored on a NAS, which I can connect to through AFP by connecting to afp://<ip address>:<name of volume within NAS> from the "Connect to Server" option in Finder. If I take that address into Automator and add a "Get Specified Server", followed by a "Connect to Server" and hit the Play button, it works fine. If I save the Automator flow as an application and run it by double clicking in the Finder, it runs fine.

If, however, I add the application to Users and Groups as a startup item and restart the computer, the action throws up a dialog reading "There was a problem connecting to server <ip address>". If I dismiss the dialog and double-click the application myself, it runs perfectly fine, which suggests it's not an issue with the Automator flow.

I've tried everything I can think of: I've replaced the "Get Specified Server" flow with an Applescript flow which mounts the server; I've tried adding a 30 second delay at the start of the flow, hoping that maybe the system was still in the process of booting, and I've even tried creating a *different* Automator flow that just opens the first Automator flow. They all have the same results: it runs perfectly fine, except if it's a startup item.

A couple of other points of information:

-I've tried adding the shared volume to my startup items, and it won't mount that way on startup either; no errors or dialogs, it just doesn't do anything.

-Neither the NAS nor any network infrastructure is power cycled at the same time; only the mini is being rebooted

-There are about a dozen more elements in the Automator flow after the mounting part, and they all run as expected.

Anyone have any insight and/or suggestions as to why my system is being so picky about automatically mounting a network share at startup? Thanks!