Great approach and great solution!
This is almost certainly a very simple fix. Check that after you assign it an IP address you have disabled BOOTP/DHCP in the module.
I can't be sure on the 1747-AENTR specifically, but on a lot of other AENTR modules there are also specific combinations you can set the addressing switches to, which will do various things on a power cycle (like factory reset). Check the position of those switches as well, assuming they exist on this particular module.