Hello,
I see you are using nginx reverse proxies (checked with wappalyzer extension). I ran into something somewhat similar on product pages, except that I would get a 502 bad gateway error from nginx, which wasn't very helpful. The problem might be that your nginx proxy header buffer is too small. The header contains metadata that is sent with every HTTP request, this metadata includes cookies, which are used for the customer's login session, keeping them logged in.
If you have SSH access to your server, you can check the proxy error log for the "upstream sent too big header" error. A path to the error log file might be:
/var/www/vhosts/designinfo.in/logs/proxy_error_log or something similar.
You can use the tail command to check the last few lines in the log file:
$ tail /var/www/vhosts/designinfo.in/logs/proxy_error_log
If the error is there, try to search it on google for a fix. An article I found with a potential fix: https://www.cyberciti.biz/faq/nginx-upstream-sent-too-big-header-while-reading-response-header-from-upstream/
The fix in the article requires that you add directives to the nginx proxy config that will increase the default buffer size. Naturally, you will need to restart the server when you change its configuration. If you are using plesk or cpanel to manage your server, I would recommend editing the nginx config from there instead as they usually restart the server for you. In plesk, it should be in the Apache & nginx settings section.
I hope this was helpful.