So I got my 7260AC replaced and same issues.
I've been doing a bit more research whilst waiting for the new card and did the following (with the new card) in the Advanced window of the card:
- Changed the channel width (for the 2.4GHz) to 20MHz only
- Enabled QoS Ad-hoc
The above I actually copied the settings of my sibling's new laptop (which comes with a 7260 N, with driver 16.6.0.8)
Currently on 17.0.5.8 and my AC is NOT disconnecting / slowing down. Throughputs are relatively stable, with pings ranging from 1ms all the way to 917ms. But no random slow-downs / disconnects so no complaints.
Not happy with the two odd months I spent ripping my hair out trying to figure this out. But it's going. Finally. That plus, not rich enough to get a dual-band router at the moment... But from what I hear the 5GHz works without any tweaking.