I have connected my Stack Overflow account to Tex.SE and Meta.SE: Can't login with an another device

Question

This question was migrated from Stack Overflow because it can be answered on Meta Stack Overflow. Migrated 3 days ago .

One week ago I set up this SO account. I was active on the site. Then when I went to Tex.SE and I logged on/connected using my SO account .

Now I am on a different computer; logged on to SO. But when I go to Tex.SE there is no option to login with a Connected-SO account (SO account connected to Tex.SE). I created My SO account with my GitHub account ; but there doesn't seem to be any options for that either.

Am I missing somewhere in authenticating or simply misunderstanding something? Why can't I log in to Tex.SE?

Tex.SE login window

Feel free to comment and ask questions from me.

I still get notification updates from the Tex.SE posts from the SO notifications tab/the section in the bar, but I can't reply, upvote, and mark as answers, because I can't login.

One can notice that I should/can/must answer this on Meta.SE , but I can't log in to it either :( .

Abbreviations:

1. SO = Stack Overflow
2. Tex.SE = Tex Stack exchange
3. Meta.SE = Meta Stack exchange