UploadField and FileField booth Not working with MultiForm

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<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

Silverstripe Version: 4.3.3

Question: MultiForm combined with UploadField/FileField Not working.

I’m desperate nothing works. When i use a FileField I choose a file, I get no errors everything seems fine. I get an Array like this:

[Dokumente] => Array
        (
            [name] => 12925c10-545f-4f1e-98da-8ed4853f8bd4.MP4
            [type] => video/mp4
            [tmp_name] => /tmp/phpt6IdyC
            [error] => 0
            [size] => 3451545
        )

but when I try to load the file there is none. file_get_contents just gives [Warning] file_get_contents(/tmp/phpuVMSbR): failed to open stream: No such file or directory

So I tried to use UploadField an I get nothig at all. Testet it with RequiredFields and couldn’t even submit the Form because it say I have no file selected but I have! I tried different Files in Different Browsers nothing works. I’ve updated everything to SS4.5 still nothing works.