Experienced this first hand. Had a crappy WiFi connection at home, started to investigate and found out that signal qulity degraded a lot when my Seagate SDD was connected on USB3.
Does "flaky" here mean connection going in & out vs inconsistent & bad speed?
Assuming we're talking about speed rather than the connection itself, two walls can be a challenge if you're on 5ghz depending on the quality of your router & dongle. Do you have any old devices on your network? Your WiFi router will run at the speed of the slowest client. Can't recall if camping is a problem - I'm less clear about the details here, but it should be. If your 802.11AC dongle is on the same frequency as 802.11N, performance will be degraded off the bat so consider moving those devices onto a different frequency if you have a dual-band router (e.g. wireless printers or older wireless TVs can be causes).
If the connection itself is flaky, check if the RSSI is really bad. Anything >= -70 dBm is good & anything <= -80 dBm is pretty bad. Note the negative sign. -90 is worse than -80. If you're on 2.4Ghz you could also be having issues from poorly shielded electronics (e.g. old microwaves) or cordless phones.
Hope this helps!
https://usb.org/sites/default/files/327216.pdf "USB 3.0 Radio Frequency Interference Impact on 2.4 GHz Wireless Devices"
Yes, USB 2 or 3 can cause issues for 2.4 Ghz if you don't shield your components properly. Are you saying that WiFi dongles, whose only job is to connect to these networks, isn't shielded properly?