There could be several reasons why your instance is stuck in a restart or suspended state. If you look here and here, it will provide you with some of the most common issues you might face.
It is also a good idea to access the Cloud SQL instance from the Cloud Shell with the gcloud debug flags to provide you with as much information as possible to resolve the issue.
Please note, do not share the output after using the debug flags unless you redact all identifiable information.