Your nslookup results for web.whatsapp.com are identical, regardless whether resolution is forced through your Pi-hole at 10.2.1.8 or a public DNS resolver at 1.1.1.1.
In other words:
Pi-hole is not blocking that domain.
Therefore, for Pi-hole to be involved, any irregularities you observe in conjunction with browsing web.whatsapp.com must implicate other domains.
How do I determine what domain an ad is coming from? may help in finding those.