WordFence scan fails: “The current scan looks like it has failed.”

I get the following error:
“Scan Failed
The current scan looks like it has failed. Its last status update was 12 mins ago. You may continue to wait in case it resumes or stop and restart the scan. Some sites may need adjustments to run scans reliably.”

I refer to the other comment and follow it.

Go to your Scan > Scan Options and Scheduling page and locate the “Performance Options”
Set “Maximum execution time for each scan stage” to 20 on the options page
Click to “Save Changes”
Go to the Tools > Diagnostics page
In the “Debugging Options” section check the circle “Enable debugging mode”
Click to “Save Changes”.
Start a new scan
Copy the last 20 lines from the Log (click the “Show Log” link) or so of the activity log and paste them here

Here is the Log

[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/kriswallsmith/assetic/src/Assetic/ValueSupplierInterface.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/kriswallsmith/assetic/src/functions.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/AUTHORS (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/LICENSE (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/README.md (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/appveyor.yml (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/composer.json (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/AES.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/Base.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/Blowfish.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/DES.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/Hash.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/RC2.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/RC4.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/RSA.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/Random.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/Rijndael.php (Mem:248.0M)
[Jun 10 04:46:36] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/TripleDES.php (Mem:248.0M)
[Jun 10 04:46:37] Scanning: /oliveunion/www/wp-content/plugins/updraftplus/vendor/phpseclib/phpseclib/phpseclib/Crypt/Twofish.php (Mem:248.0M)
[Jun 10 04:46:37] Calling fork() from wordfenceHash with maxExecTime: 20
[Jun 10 04:46:37] Entered fork()
[Jun 10 04:46:37] Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 4198400 bytes) in /oliveunion/www/wp-content/plugins/wordfence/lib/wfConfig.php on line 691 The site is experiencing technical difficulties.