So I have this filly who is ToTo yet her tobiano didn't come up at ALL

I have had this same problem with several of my foals as well. I will try and find links but they are scattered throughout my barns so I don't know how successful I'll be.

Can you link to the horse?

Looks like it's this foal, Eve

That happens a ton with my horses, especially since I breed for the frames and tobis.

Not my horse but just bred to her and she is missing her tobi

It might be a non visible gene

No, it's a bug. There is no non-visible tobiano.

I found one, ToTo. There must be something wrong with a certain ToTo pattern layer.

Here's another one... also ToTo