What if the spider doesn't come because of the revision?

The website has been revised. After the revision, the traffic has dropped, and the spiders have stopped coming to the website, which has caused me to update more or less useless. How can I optimize the website and restore it to normal? Why do many problems occur in the revision? What is the reason? What can I do to solve the website after the revision if the spiders do not come? What are the better optimization methods?

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