UltiSnips not work all the time

Question

I have configured UltiSnips for vim as described in the documentation of UltiSnips

" Track the engine.
 Plugin 'SirVer/ultisnips'

" Snippets are separated from the engine. Add this if you want them:
Plugin 'honza/vim-snippets'

" Trigger configuration. Do not use <tab> if you use 
 https://github.com/Valloric/YouCompleteMe.
let g:UltiSnipsExpandTrigger="<tab>"
let g:UltiSnipsJumpForwardTrigger="<c-b>"
let g:UltiSnipsJumpBackwardTrigger="<c-z>"

" If you want :UltiSnipsEdit to split your window.
let g:UltiSnipsEditSplit="vertical"

Except that I am using vim-plug and the directory for the plugins is ~/.vim/bundle.

My problem is that it seems as if my snippets won't get triggered every time. I have a test snippet in my all.snippets which I can't execute. But I have added another trigger in my html.snippets which I can execute in html files. I then tried to save a snippet in the vim.snippets which again cannot get executed or triggered. Is there another thing I have to configure?

Although I have added let g:UltiSnipsEditSplit="vertical" to my .vimrc, it just does not want to start my /ultisnips/<filetype>.snippets in a vertical window it always starts in a seperate vim buffer.^

Edit:
Here is my real .vimrc

call plug#begin('~/.vim/bundle')

Plug 'honza/vim-snippets'

Plug 'lervag/vimtex'
let g:tex_flavor='latex'
let g:vimtex_view_method='zathura'
let g:vimtex_quickfix_mode=0
set conceallevel=1
let g:tex_conceal='abdmg'

Plug 'SirVer/ultisnips'
let g:UltiSnipsExpandTrigger='<tab>'
let g:UltiSnipsJumpForwardTrigger='<tab>'
let g:UltiSnipsJumpBackwardTrigger='<s-tab>'
let g:UltiSnipsEditSplit='vertical'

call plug#end()

I have created an html file and added some snippets for html files. These snippets work. Then when I try to add some snippets to my all.snippets file which should be executed no matter in what kind of file I am, if I get that correctly. But this is not the case. Only one snippet file seems to work.

I have found out something about this problem: My test html file is in ~/Projects/learn_vim/testing.html. When I use the :UltiSnipsEdit command, it does not place the html.snippets file where it is usually placing my snippet files: it placed it at this location: ~/Projects/learn_vim/UltiSnips/. And this file seems to work.

So I checked it further and it actually seems like it always creates an folder in the directory I am in with the snippet files. Could I just define one place for all my snippets?

Also I have found out what my "vertical" problem was, see my .vimrc :)

Thank you for the patience