I've launched Wireshark monitoring DNS traffic of roughly 5 phones. I've collected 19.8k DNS packets so far. Out of that, 5.1k packets are flagged with REFUSED or SERVFAIL. If I am not mistaken, it means that 51% of DNS requests fail.

Looking at queries for graph.instagram.com, it looks like there are roughly 20 attempts in a sequence before it gives up.

All in all, this could probably explain doubling of the DNS traffic. But the sample is rather small, so take it with a grain of salt.

5.1 / 19.8 is much closer to a quarter than to half. But your point is still just as poignant at ~25% as it is at 51%.

I think those are DNS round trips. So 1 packet to request and 1 to respond. E.g. 9.9k total requests of which 5.1k fail.