Cannot access shared file

It sounds like you're attempting to call /2/files/get_temporary_link on a file that has been individually shared with you, i.e., a "received" file, such as listed by /2/sharing/list_received_files. As this isn't mounted anywhere in your account, this 'path/not_found' error is expected, since the file is not available in your account's file/folder structure and so cannot be accessed that way. This would also apply to /2/files/download. Adding a shared folder containing the file mounts that shared folder in your account, making the file available in your account, so the calls can then succeed.

I don't believe this behavior changed recently. You can instead use /2/sharing/get_shared_link_file and pass in the "preview_url" (e.g., from /2/sharing/list_received_files) as the "url" to download the file though.