Hm... you might want to try to downgrade to the recommended Forge version 2491.
But I do not think that will fix your problem, because I cannot reproduce the issue with any 1.12-forge version I tested (including 2503 and 2491).
I would need you to post the startup-log so I can see, if I spot any issues there...
I'd need ./logs/fml-client-latest.log
I can't find that Option, tough. I got nothing like Chunk Loading = Smooth / Default in my Options.
I'm also wondering why yours is the only invisible block :( As you saw, i got somehwat 160 Mods installed, and mone got problems. Seems like i have to try around again with removing mods in bulk, urgh.
I'm using C6. You're right, the Chunk Loading option was for a past version (probably for 1.7.10) so never mind that...
Thing is I am not using OptiFine very often and I don't know about all the options and so on. You may wanna try a separate, clean installation with just OptiFine on default settings and Disenchanter to see if it works there.
If not I'd guess it's some stupid graphics card problem... It's just wierd that this only happends to the Disenchantment Table. It uses the a copy of the model of the Enchantment Table.
Granted the texture location is a bit unusual (see #12), but since the item loads no problem AND I do not see any texture loading issue in the log, I do not think that's the issue.
I'm at the Moment tracking it down to the mod that causes this behaviour and am hoping you can help when i managed that. I have nailedd it down to 5 mods. I'll tell you which one causes that when i'm done.
You might wanna try to disable the animation of the Disenchantment Table in FBP (maybe there is a config option? At least there is supposed to be an option...).
Because maybe it might take some time until this will be fixed.