disabling ipv6 had no effect.
i'm trying to install batman: arkham city - it appears to download the entire file (17.63GB/17.63GB) but still shows a download speed that fluctuates b/w 22 MB/s and 27 MB/s.

conversely, i was able to download and install batman: arkham knights without any issue (prior to disabling ipv6)

and yes, i'm sure i have space, there are > 2 TB of space on the installation drive

This is the same for me, trying to download Witcher 3 and stuck at 92% and yet it's still downloading something at 20Mb/s or so, been like this for about 24 hours. I do have IPv6 disabled and tried to restart computer/GOG/the download several times, same every time.

The offline installer downloaded just fine though, if I install from there do I still get trophies and such?

Gog is all screwed up at the moment. It seems it's a regular thing now Gog is a mess.

After all the years Galaxy still is an utter pile of crap. I'm trying to download Spaceengine but the darn thing hangs at 69% for hours now. Restarting Galaxy does not help. It seems Galaxy has become even worse over the years. I had issues like this with many downloads. I think I'll refund the game here and get it on Steam instead. I never had any download issues on Steam. Why is it so difficult to create a similarly reliable client?