I have a similar issue, except that I'm using Sailfish 2.0.4.13 on a OnePlus One, and I turned off developer mode to troubleshoot a network issue and when I attempt to re-enable it it says: 'Developer Mode requires a Jolla account'.

I have a Jolla account, but can't use it on my One since it's a community port and that's just dirty. So if I try to add the account I get an IMEI not saved error.

Trying fingerterm from openrepos, developer mode is quite gone. Command 'devel-su' gets a 'command not found' error

But I'd had developer mode enabled. Can I get it back short of a reflash? Ideas?