Cannot read properties of null (reading 'headersReady')

[userxgl]

Multi-page pdf preview exception after build.
{
message: "Cannot read properties of null (reading 'headersReady')",
name: 'UnknownErrorException',
details: "TypeError: Cannot read properties of null (reading 'headersReady')"
}
In the development mode is OK, Is there a problem with the build?

[cleverpig]

MARK