Either construction (gerund or to+infinitive) is fine, though the 'to hear' version is probably more common. The main problem is the collocation 'incredibly lovely', which doesn't sound natural. I'd just say: It's lovely to hear from you again. It's lovely hearing from you again. If you want to add emphasis, you could use 'so' or 'really'.

2.- It is incredibly lovely to hear from you again

I think After it is + adj we should write to verb It is incredibly lovely to hear you again Please, Native one , come here and learn me:-):-):-):-):-)

They both sound fine to me, although starting with a contraction sounds more natural - "It's incredibly lovely...." rather than "It is incredibly lovely..."