Debugging CF7. The form worked, and then stopped. What could be the problem?

Question

WordPress

Hello. The form was made in CF7, it worked until yesterday evening, although it’s not a fact that it’s 100% correct.
Before the obvious problem, the following actions were taken:
Yesterday I updated the Jetpack plugin from WordPress.com
Yesterday I updated the Yoast SEO plugin
Yesterday I added new training courses to the form template (standard changes are made according to the template, the form has always worked).
Earlier, the day before yesterday, I updated the engine to 4.9.4.
By itself, the form seems to send, but the letters (applications) do not come. The CF7 version is the latest (5.0).
Page with the form https://engineer's blog/training