Since you’re using WP Fastest Cache on your site let’s try this:
Go to WP Dashboard > WP Fastest Cache
Click on the Clear Cache tab
Under the Time Out section, create a rule (if you don’t have one already), set If Request_URI to All, and select the Once Every 10 Hours option from the dropdown below.
Click on Save to save changes.
Click on the Clear All Cache button to clear W3 Fastest Cache’s cache so changes are applied immediately to your site.
Hopefully after that your popular posts list should load normally. If it doesn’t please let me know and I’ll have another look.