Having the same exact problem. I log in, good ping for a short period of time then slowly climbs until finally disconnecting me. I D/Ced about 20 times in an hour. Disabled addons, rebooted computer and router multiple times, and still having the same problem. Issue seems worse in high population areas and raids.
Edit: I'm wondering if Google DNS settings would cause this? Nevermind that. Nothing changed after changing DNS settings.
Edit 2: I'm not wondering if the recent Windows Update could have rerouted something? I'm hitting firewalls with and without using a VPN. Quite frankly, I'm no expert at this stuff, but that Windows Security definitions update recently was the only thing that changed for me in past few days.