I have been having a strange problem sending certain kinds of data using Google's services. I can't sync using Google Drive nor can I use any captchas (I click the pictures it tells me to, but when I send my response I get an error message). Incidentally Windows Update isn't working, either (I've been getting the 80072ee2 error), which might be related. I used to not be able to attach files to Gmail or upload to Drive, either, but that fixed itself for some reason.
The problem started back in November 2015. I think it has something to do with me messing around with Windows Features, but I've double-checked those and I can't see what's wrong. Is this a packet issue, or DNS?
EDIT: Decided to poke around with Wireshark (though I am very much uneducated about it) and take a capture while I tried to get Windows Update to go.
It seems that I'm getting a lot of "TCP ACKed unseen segment" errors, with my PC as the destination. I think for some reason I'm not able to receive any ACKs from the external server. Lots of FCS errors too.
This might just be an ISP issue as well; we use Telus and apparently they'd switched on IPv6 right around the time I started having problems.