I found the reason, the latest version 5.2.1 conflict with plugin ” Contact Form DB”. Now I disable Contact Form DB, everything goes well.
Autoptimize
Category Order and Taxonomy Terms Order
Contact Form 7
Contact Form DB
Easy FancyBox
EWWW Image Optimizer
WP Mail SMTP
Yoast SEO
Above are all plugins on my website. They work together for quite a long time, always no problem until I update contact form 7 to lastest 5.2.1.
thanks for your reply. The website is: https://www.acrylic-frames.com, you can test from any of product pages. For example: https://www.acrylic-frames.com/product-detail/acrylic-frame-wall-mount-afl-034/ or contact page.
