Tested in a fresh client with only Colytra and JEI.
The Toggle Elytra keybind doesn't do anything (and its not conflicting with anything, as its the only mod).
Tested with different keybinds in our modpack that still runs Colytra 1.0.1, to no avail (didn't see this mentioned in the changelogs)

Just for clarification, have you only tried version 1.0.1? I don't think I changed anything about this between versions, but I just want to make sure I have the right information.

Only tried different keybinds on 1.0.1.
The standalone client was with 1.0.4.1

I should have clarified :P

I've successfully replicated the bug and am currently working on a solution.

Nevermind, I made a mistake due to a lapse in judgement. I cannot actually replicate this bug, it works fine for me. I'd like to make sure you're referring specifically to elytras attached to chestplates and not regular standalone elytras, as the latter is not affected by the keybinding at all.

I think I may have misunderstood the "Toggle Elytra" feature then.
After you mentioning the chestplate attachment, I now see exactly what it does.

What I thought it would do, was Activate/Deactivate the Elytras flight (thus toggling it), like EnderIOs Dark Steel Armor can do in 1.10.2.
Which would be a handy feature as well, due to Cyclics multijump enchantment :)

But I guess that settles it

It does activate/deactivate elytra flight, but only for elytras attached to chestplates. If you turn it off, you cannot fly. It just doesn't do anything for normal elytras, although I could change this if so desired.

I would see it as a desire, so I don't have to pray that the server actually catches that I want to enable the elytra :)
Also having control when to deactivate it is always nice, if it's not attached to a chestplate (bauble ftw), so you don't have to faceplant the ground

Was this ever fixed with bauble elytra's? When i use the bauble one in 1.12.2 it only activates with spacebar and not the button i assigned the hotkey to..