This does happen quite a bit. Depends on the SERPs. Many times, you have top 10 results, where a good portion of the SERPs have been there for 5-10-15 years. Their algo isn't just going to let you barge right in. The key is to continue building, fine-tuning the on-page, adding supplemental content for interlinking, etc.. I also find it beneficial to let the SERPs breathe. Sometimes I'll hit pages with links hard for 3-4 months, then take a month or two off. Rinse and repeat once the SERPs start getting stagnant.