Indexing increase after traffic surge

I run a job board that has been live for about a year. While it doesn’t have many backlinks, it is indexed on Google—I can find it by searching its name. Each individual job page is structured with job posting schema. As of today, Search Console shows only 4 Valid jobs out of over 1 million pages. A couple of weeks ago, the website got a significant traffic surge, which led to a spike in indexed job postings—from around 200–300 to nearly 60,000. However, a few weeks later, the number of indexed pages dropped down to ~100, eventually nearing zero. This pattern repeated recently: a smaller traffic surge led to an increase in indexed pages, but then the numbers declined again. Is this fluctuation normal? I attached an image in the comments.