New server have a bug, help please

Hello!

I used this server about half year, and all was ok. But from now i lost possibilities to upload and link Custom thumbnails for my video files. Thumbs files are guranteed ok, i use them before many times, and on this server too.

I selecting
Custom Thumbnail
Upload a JPEG image to use as the thumbnail for this item.
Image does not need to be thumbnail size; it will be resized as needed.

and after it i see
Changes saved successfully without result, i see default thumbnail.
I attach 2 pages of Debug info, please, help me if you can.
Thank you!