Files starting with eZ_REST_BinaryFile are created when uploading a binary (e.g. ezimage field type).

Those amount of files keeps growing and taking up huge amounts of storage.

Especially on Platform.sh this directory is not cleaned when deploying a new version. The files have to be removed manually at the moment.

As soon as the disk is full, the system is no longer usable (binary upload, sessions, etc).

PS:
The files are created twice. The upload of one image created those two files in my test:

-rw-------  1 web  web  374148 Oct 13 12:05 eZ_REST_BinaryFileWCe910
-rw-------  1 web  web  374148 Oct 13 12:05 eZ_REST_BinaryFilevnXZPt