Hello. Perhaps the situation is related to the increase in the size of the downloaded file. These may be hosting restrictions. Write to their tech support.

In the settings of the form field, you can yourself specify which file extensions you want to allow to attach.

thank you for reply,

 already change hosting service due to restrictions,and choose the VPS, for my own,

alternatively:

how to add in to contact form about " size limitation warning?" if the clients file is large

(as  like gmail; atachment file is too big warning and divert to gogle drive automaticaly)

or

instead of java error report redirect to another page with warning as like;

" your video is too big to post, please reduce it and send it again"

message.