Hi sohaibnoyyan19 ,
Apologies for any inconvenience caused.
Unfortunately, I can't figure out what you are talking about, sorry. No sub-entity can be added anywhere.
Are you telling me you're loading a default template, and it gets stuck with a timeout error? If so, which template?
Or maybe you are creating a template from the scratch, and you select the format of the export file, but it gets stuck when you try to select the Main Entity?
A screenshot would help. If you don't feel comfortable publicly sharing info from your site here, please, open a private ticket here.