And I'm back, hopefully with something equally as idiotic and easy to resolve, although I've had a nose and can't find anything that stands out as obvious.
Inspector now loads - I believe as it gets the same readout as everything else ([Server] Server thread/INFO [FML]: FML has found a non-mod file Inspector-0.6.3.jar in your mods directory. It will now be injected into your classpath. This could severe stability issues, it should be removed if possible.) - but it has no commands registered. There's nothing that actually shows it as loading.
The only thing that looks like an error to me is this:
[21:52:53] [main/ERROR] [FML/]: Unable to read the jar file spongeforge-1.8.9-1890-4.2.0-BETA-1522.jar - ignoring
But as things actually load ... I can't see it being that. Although I am pretty much just a jovial idiot when it comes to this.
Logs removed to lower page consumption.