Hello there,
Thanks for contacting us and I hope you’re doing well ??
Maybe another plugin or your theme is in conflict with our YITH WooCommerce Wishlist and it’s taking some time to update_wishlist_count
I suggest to try to deactivate all plugins, leaving only WooCommerce and YITH WooCommerce Wishlist active, and see if the problem is solved. If so, try to activate them again, one by one, to see which one causes the issue.
If the problem isn’t caused by a plugin, try to activate the default theme Twenty Sixteen and see if you have the same issue.
Also, if you have customized some files in your theme, please try with a fresh installation without any customization.
Please try this solution and let us know what issue shows.
Have a good day.