It may seem a little obvious to some but it was an oversight on my behalf.

If you are adding files to the zip file that you want to be deleted make sure you delete AFTER you call the close() function.

If the files added to the object aren't available at save time the zip file will not be created.

If you're adding multiple files to a zip and your $zip->close() call is returning FALSE, ensure that all the files you added actually exist. Apparently $zip->addFile() returns TRUE even if the file doesn't actually exist. It's a good idea to check each file with file_exists() or is_readable() before calling $zip->addFile() on it.

ZipArchive.close() changes its behaviour in PHP7. The function ignores directories in PHP5 but fails in PHP7 with: 

Unexpected PHP error [ZipArchive::close(): Read error: Is a directory]

The following code works in PHP5 but not in PHP7:

<?php 
// test.php
$zip = new ZipArchive();
$zip->open('/tmp/test.zip', ZipArchive::CREATE);
$zip->addFile('.', '.');
$ret = $zip->close();
echo "Closed with: " . ($ret ? "true" : "false") . "\n";
?>

For php5:

php --version
  PHP 5.5.38-1-avature-ondrej-fork (cli) (built: Aug 31 2016 16:37:38)

php test.php
  Closed with: true

For php7:

php --version
  PHP 7.0.8-0ubuntu0.16.04.2 (cli) ( NTS )

php test.php
  Closed with: false

If you have created a zip file and added a file to it without error, yet the ZipArchive::close call fails (with ER_TMPOPEN: "Failure to create temporary file") and the zip file is not created, check to see if your ZipArchive::open call specifies a pathname containing nonexisting directories. If you expect a containing hierarchy of one or more directories, you must create them yourself before using using ZipArchive. You can write a simple function to recurse using dirname to find each parent directory, creating those that don't exist by using mkdir when leaving the recursion.

I am not sure, but seems that $zip->close() can run into errors if the path specified in $zip->open is a relative path, not absolute.
So, when create archives, please specify ABSOLUTE PATH, not relative path for zip file to be created.

Don't forget to check the zip isn't empty, folks - otherwise the zip won't be created at all, and the server will issue no warning!

I used a certain loop to add files to the zip, and struggled with permissions and documentation for hours before I realize the loop ended up adding no file, even though addFile WAS called, but on a non-existent file.
This might be the reason your zips aren't popping up.

If you get an error like "ZipArchive::close(): Renaming temporary file failed: Permission denied" at random times, check your antivirus software (e.g. Trellix), which may block writing while scanning the file. In my case, I had to check with flock until file is unlocked.

Pay attention, that ZipArchive::addFile() only opens file descriptor and does not compress it. And only ZipArchive::close() compress file and it take quite a lot of time. Be careful with timeouts.