Instructables web site login fields do not show

  1.  Startup in Safe Mode and test.

       Launch Safari and test.

       Restart normally by clicking the “Restart” button at the bottom.

       Start up in Safe Mode. https://support.apple.com/en-us/HT201262

  2.  If this doesn’t help, download EtreCheck, https://etrecheck.com/maspro  and post the report here.

      Click  “Click to download” button,

      Open Downloads folder, click on it to open, and then select ”Open”.

      “Choose a problem” from the popup menu box, and then “Start EtreCheck” in the dialog.

      Click “Share Report” button in the toolbar, select “Copy report” .

      Paste the report when you reply.

      Note:      This is a diagnostic test.

      If 5000 words limit applies: Split the report into two parts and post as two separate posts. 

As a test, also try setting up another admin user account to see if the same problem continues.

Isolating an issue by using another user account 

I didn't see any login/sign in prompt.

However there is a Related Links link that took me to Ad Sense login page.

Try suggestions given here.

If features on a webpage don’t work in Safari on Mac