Can you please share your form to look into?

Can I see your form?

Please select the Root element correctly while uploading the schema or the schema you are using in your form.

From the logs seems like your schema is not valid, are you using json or xsd file? Need to check your schema.   Caused by: com.github.fge.jsonschema.core.exceptions.ProcessingException: fatal: content at URI "crx:/content/dam/formsanddocuments/schemas/schema.xsd#" is not valid JSON     level: "fatal...

try this:<span style="color:Red;">Hello ${firstName} ${lastName}</span>  

Use the below script code in the initialize event:   this.validate.nullTest = (this.rawValue) ? "" : "error";

You can give left, right, top, and bottom margins in the subforms as per your need.

See the images of how I changed the highlighted to flowed and wrapped the positioned subform inside the flowable subform and it worked.  

Have you made the Main page flowable and allowed pagebreak in all flowable subforms and on the main page?   If it still doesn't work, share your form. I'll look into it.

Yes, that's the case with the positioned layout. You can do one thing if you do not want to change every subform to a flow layout, then let it be positioned and wrap them under a subform with a flowable layout.