- Could it be that there was a difference in IPv6/IPv4 presence/preference between the two? E.g. your wired connection acquired an IPv6 address while the wireless was IPv4 and had to go through NAT.
- Did you make sure to compare results for non-concurrent speedtest? Ie maybe those ~800 were actually 4x~200 - many speedtests open parallel connections by default.
- The speed test difference was consistent no matter the measurement tool - speedtest.net, fast, actual file transfers, etc.
We got pretty far down the rabbit hole with diagnostics. TP-Link actually spent a significant amount of effort supporting me - had a debug firmware doing packet captures, testing different hardware acceleration settings, sent me multiple routers with different chipsets, etc.
I brought the hardware with me when I moved and I do not have the issue.
Aside from TP-Link consumer segments being unreliable and buggy - I wonder if TTL comes into play here. I know some mobile ISPs have been throttling or block traffic based on packet TTL (as a proxy for tethering) but it's not something I've heard of otherwise...
I haven’t had issues with my hardware from them, I confirmed the behavior with non TP-Link hardware as well, for what it is worth. I was actually impressed I ended up taking to an actual product engineer.
- Did you make sure to compare results for non-concurrent speedtest? Ie maybe those ~800 were actually 4x~200 - many speedtests open parallel connections by default.