Hello,
I found the solution for my problem. We upgraded the Moodle from 2.8 to 3.3 last semester but used the config.php of the old moodle version. Therefore the layout of the new Moodle version got disturbed. Adding the parameter '$CFG->defaultblocks_override' in config.php following the below link solved the issue.
https://docs.moodle.org/33/en/Block_layout
Thanks,
Shubham