My spouse and I are having the same issue, we have tried the fixes and nothing has completely fixed it. It's becoming more random, either happening to a few seconds longer or having more time in between spikes..

Are you using a VPN? No for both
Are you using a wired or wireless connection? Wired for Spouses comp, Wireless for mine
What Platform are you using? (Steam/Windows/Mac/PS4 etc.) Windows for both
Does the issue occur with one character or multiple characters? Multiple characters for both
At what point do you get disconnected and/or are unable to connect? Never disconnected for both, lag spikes every 1-3 minutes but times are random and lag can last longer than 2 seconds. It is inconsistent but almost only happens in instances.
How often does the issue occur? Been happening since last week, happens constantly with only few breaks

Internet Service Provider: Google Fiber
Region/State: NA/Texas

All steps taken to resolve the issue: Done everything everyone else has done before this post