Hey, I've DM'ed you with a video of me trying to log in.

Is there some kind of flag or certificate on my computer I need to reset or delete?
I feel like that would be the only reason it wouldn't work at this point.

Just downloaded it, still have the same issue. Is there some kind of temp files or cache I need to delete?

When ever I try to open Cubik Pro (MC18) and enter my details no matter what it will give me;
https://i.imgur.com/Ye0GSlp.png

I can enter the exact same details into my cubik studio and it will work fine, I understand that Cubik Pro is outdated and unsupported but I need to use it for the 1.8 ...

You need to use RShift rather than LShift since its used for scaling and not selecting

So the issue I think your having is that when you created a model for the bow, you replaced all the overrides for the pulling animation.
{
"parent": "item/generated",
"textures": {
"layer0": "items/bow_standby"
},
"display": {
"thirdperson_righthand": {
"rotation": [ -80, 260, -40 ...

You just need to disable element shading or set all of the element shades to white.

You need to check if you texture name is all lower case, and is pathed correctly.

Tools>Preferences>UI

Culling is in reference too Minecrafts culling system were it removes faces that wont be seen when blocks are placed. Its not in reference to the amount of faces on the model its self. If you want to optimise it you need to click the one next too with the x symbol, but if your model is just 2 simple ...

Try resetting everything, and if that doesn't work then just export them as OBJ and upload them manually.