Scan not completing. Conflict with W3TC

Hello,
I just installed WordFence as I was having the server crash due to bruteforce attacks on wp-login and xmlrcp.php. During a scan with WordFence, this came up (scan stuck here for several minutes and never finished):
[Nov 01 03:02:56] Notice: Undefined index: HTTP_REFERER in /home/domain/public_html/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php on line 366 Notice: Undefined index: HTTP_REFERER in /home/eas

So I went to the W3TC plugin and disabled database caching, and then ran the scan again and got this:
Nov 01 03:28:55] Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 5987 bytes) in /home/domain/public_html/wp-content/plugins/w3-total-cache/ObjectCache_WpObjectCache_Regular.php on line 200

On this page help page:
https://docs.wordfence.com/en/My_scans_don%27t_finish._What_would_cause_that%3F
I see:
“Go to the Wordfence Diagnostics page.
Scroll toward bottom where you’ll see an option to specify the maximum memory that Wordfence uses.”

However, there is no option to specific or change the Memory limit on that page that I can see. Are the instructions out of date or is it my installation?

What’s the best way to resolve this issue? Ideally I’d like to keep database caching enabled, but need to secure the site first.

Thanks.