Hello Joshua,
The most likely reason why you do not see it on the Service Account page is for the Compute Engine service to have been deleted. I have reproduced this scenario on my end and saw the same thing as you on both pages when deleting the account. The Compute Engine service account is created automatically once the Compute Engine API is enabled and nothing stops you from either deleting the service account or removing it from your IAM policy. Note that your IAM policy is not affected by the creation and deletion of accounts. You can figure out how this happened by checking the Activity tab on your dashboard so you can see by whom and when the account was deleted.
To create a new account, simply disable the Compute Engine API and re-enable it on the API & Services page and that should create an account for you on both pages. You can also contact the Compute Engine team to add the account back to your project.