The following 2 configuration settings are planned but not implemented:
Enable/Disable AMP HTML validation without uninstall/disable
"amphtml.validator.enabled": true|false // Default: true
Keep/Remove AMP HTML validation errors after closing the document
"amphtml.validator.keepIssuesAfterDocumentClose": false //Default:true
The issue is how the VS Code fires onDidChangeContent() and onDidClose() events when user clicks away from PROBLEMS panel and activates again PROBLEMS panel. (Reported in latest VS Code version 1.26.0). Due to this issue, the document is re-validated every time user focuses back to PROBLEMS panel.
Debug or create a bug on VS Code to figure out why and how to resolve this.