Loopback taking too long

I use these two plugins:
Login Widget With Shortcode, Version 5.6.4 and WP Register Profile With Shortcode, Version 3.3.7

I ran Health Check by the www.remarpro.com Community. It found that both of these plugins have loopback problems.

Here is the message I received for both plugins:
The loopback request to your site took too long to complete; this may prevent WP_Cron from working, along with theme and plugin editors.

How do I fix this problem?

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