“Nonce verification failed” when creating comments

I have a simple blog. I’ve been a happy user of WP Fastest Cache for years (including the premium upgrade).

However, starting a few months ago, visitors to my blog have been getting the error “Nonce verification failed” when leaving a comment. It looks like this: https://www.dropbox.com/s/jojkq1xi5jxvugx/screenshot%20of%20error.PNG?dl=0

The error goes away immediately when I disable the WP Fastest Cache plugin.

Last month, I disabled the WP Fastest Cache plugin and immediately reactivated it. It appeared to fix the problem temporarily. However, after a few weeks the problem resurfaced.

Any suggestions? Thanks!!!!