I am active on
philosophy.stackexchange.com, but can no longer log into any of them. I presume this is because I am logged into other Stack Exchange sites (where I am also active) under another login name.
This has never been a problem before but it seems to have become one under your new login procedures.
The only way I can log into math, physics and philosophy sites (and now meta) is to open a separate browser.
I am certainly not going to be willing to do this very often, therefore, unless you fix this, I won't be back. I do hope you fix it.