I temporarily Paused it with intent to Resume after, somehow Start/Resume doesn't work and instance is suspended.
It says Internal error. Please try again or contact Google Support when I try to resume it.
I don't know much about this and any troubleshooting tips is greatly appreciated.
This feature is in beta stage that means some instability may be expected. You can try later and check if it works.
You can try resuming it using gcloud:
gcloud beta compute instances resume INSTANCE_NAMES.
If the VM won't be resumed you can run this command with --verbosity=debug flag and update your question with thre results - it may give more insight why the VM isn't resuming.
You can also report this issue to Google in IssueTracker and describe in detail everything.
