Unexpected errors, especially in Login

System info: shorturl.at/nxDEG

1. When I click to login, I go to (a) wp login page or (b) An error like 404 or simply refresh page.
Ignoring (b) because it comes to (a) after refresh.
When I login there are multiple things that happen –
1. I reach the homepage without being logged in and I have to sign in again
2. I reach the homepage without being logged in, which means login button is still showing which would have turned log-out if I had signed it. But, now when I click on login, I reach the dashboard. There is no logic to this…
3. I am unable to open my dashboard sometimes as the 404 warning page comes.
Also, sometimes I am unable to edit the plugins, it says link expired and at other times it simply does save the settings I have changed. I am unable to deactivate plugins now.
And other minor here and there, but once logged-in, the site is working and I am able to setup the smaller parts.
An hour back i used this on the wp-config to repair the config via FTP – define( ‘WP_ALLOW_REPAIR’, true );
But the repair link did not detect the line.

The page I need help with: [log in to see the link]