I lean toward Rob Skiba's view that there was no second occurrence, but still have questions.
THE RETURN OF THE NEPHILIM: AFTER THE FLOOD
I think it's more complex to understand the generations of Nephilim.
1 Enoch 7:2 And they conceived from them and bore to them great giants. And the giants begot Nephilim, and to the Nephilim were born †Elioud†. And they were growing in accordance with their greatness.
According to Enoch the grandchildren where the Nephilim. If the first occurrence was "in the days of Jared", then there is over a 1000 years for the Nephilim to reign till the flood when they were destroyed (though the 1st generation abominations were killed off before reaching age of 500) and we all know how long antediluvian man lived, many almost a 1000 years.
Another theory is through Canaan. Did one of the wives on the Ark carry Nephilim genes? Was Ham's sin related? Who was Canaan and who was Kanaan? Why is Arphaxhad's genealogy mixed up? Og king of Bashan
Duet 3:11. Each generation of giants was diluted by humans, but still at the time of Goliath they were still massive.