King Leo on "[Plugin: Wordfence Security] Version 6.1.12 Undefined index: coreUnknown"

Upgraded to Version 6.1.12 and ran a scan. In the middle of the scan,a pop up window appeared with this message:

An error occurred

A scan is already running. Use the kill link if you would like to terminate the current scan.

I closed the window, but did not use the kill link. The scan continued without interruption until if finished.

Here is what the log shows when the error occurred during the scan:

[Jul 26 16:55:36] Analyzed 3698 files containing 91.84 MB of data.
[Jul 26 16:55:36] Undefined index: coreUnknown (8) File: /hermes/bosnaweb10a/b611/ipw.deecasci/public_html/wp/wp-content/plugins/wordfence/lib/wordfenceHash.php Line: 141
[Jul 26 16:55:36] Starting scan of file contents

Then, here are the last lines of the scan when the scan finished:

[Jul 26 16:56:19] Scan Complete. Scanned 3698 files, 6 plugins, 3 themes, 173 pages, 0 Idea and 10742 records in 81 seconds.
[Jul 26 16:56:20] Wordfence used 7.57MB of memory for scan. Server peak memory usage was: 60.66MB
[Jul 26 16:56:20] Notice: Undefined index: coreUnknown in /hermes/bosnaweb10a/b611/ipw.deecasci/public_html/wp/wp-content/plugins/wordfence/lib/wordfenceHash.php on line 141

Any idea what caused this error?

https://wordpress.org/plugins/wordfence/