[MediaWiki-l] Re: user login issue after upgrade to 1.37.2

I successfully upgraded/migrated my old wiki 1.26.0 to a new wiki 1.37.2 about a month ago. But now I realized I couldn't log in the wiki to edit content. I was not sure what my old user password was but assuming the old password was less than 8 chars. So I used changePassword.php to reset my password and set a new one longer than 8 chars. But when I used it to log in my wiki, it seems to accept but goes back to original page with only "Log in" link on the top right corner, which means I'm not logged in. I immediately checked LocalSettings.php if $wgReadOnly was still configured after the upgrade, which was commented out with the leading '#'. What could cause this behavior of the wiki?