Below are the logs i can see.

root@secondary:Standby:In Sync] config # tail -f /var/log/httpd/httpd_errors
May  1 09:54:14 secondary.mafgroup.local err httpd[2785]: [proxy:error] [pid 2785] AH00940: AJP: disabled connection for (localhost)
May  1 09:55:43 secondary.mafgroup.local err httpd[3373]: [proxy_ajp:error] [pid 3373] [client 10.110.110.120:57952] AH00992: ajp_read_header: ajp_ilink_receive failed, referer: https://10.46.11.52/xui/
May  1 09:55:43 secondary.mafgroup.local err httpd[3373]: [proxy_ajp:error] [pid 3373] (120006)APR does not understand this error code: [client 10.110.110.120:57952] AH00878: read response failed from 127.0.0.1:8009 (localhost), referer: https://10.46.11.52/xui/
May  1 09:57:26 secondary.mafgroup.local err httpd[2840]: [proxy_ajp:error] [pid 2840] [client 10.110.110.120:58050] AH00992: ajp_read_header: ajp_ilink_receive failed, referer: https://10.46.11.52/xui/
May  1 09:57:26 secondary.mafgroup.local err httpd[2840]: [proxy_ajp:error] [pid 2840] (120006)APR does not understand this error code: [client 10.110.110.120:58050] AH00878: read response failed from 127.0.0.1:8009 (localhost), referer: https://10.46.11.52/xui/
May  1 09:58:53 secondary.mafgroup.local err httpd[2784]: [proxy_ajp:error] [pid 2784] [client 10.110.110.120:58516] AH00992: ajp_read_header: ajp_ilink_receive failed, referer: https://10.46.11.52/xui/
May  1 09:58:53 secondary.mafgroup.local err httpd[2784]: [proxy_ajp:error] [pid 2784] (120006)APR does not understand this error code: [client 10.110.110.120:58516] AH00878: read response failed from 127.0.0.1:8009 (localhost), referer: https://10.46.11.52/xui/
May  1 09:59:02 secondary.mafgroup.local warning httpd[2784]: [auth_pam:warn] [pid 2784] [client 10.110.110.120:58537] AUTHCACHE Error processing cookie CC5W2GVS4HF5AQC22IOI5SJJ5J - Failed Read: User, referer: https://10.46.11.52/xui/framework/css/xui.css?ver=15.1.5.1.0.0.14
May  1 09:59:02 secondary.mafgroup.local warning httpd[2784]: [auth_pam:warn] [pid 2784] [client 10.110.110.120:58537] AUTHCACHE Error processing cookie JMA4W5Z2RMZ4AK4WAFSF7KY2OI - Failed Read: User, referer: https://10.46.11.52/xui/framework/css/xui.css?ver=15.1.5.1.0.0.14
May  1 09:59:02 secondary.mafgroup.local warning httpd[2784]: [auth_pam:warn] [pid 2784] [client 10.110.110.120:58537] AUTHCACHE Error processing cookie T65HKU7VX63GTPUFLJEBHT6RUU - Failed Read: User, referer: https://10.46.11.52/xui/framework/css/xui.css?ver=15.1.5.1.0.0.14

Hi Preet_pk​ ,

Have you try this article:

K03531511: BIG-IP Unreachable through HTTPS

https://my.f5.com/manage/s/article/K03531511

Environment

• BIG-IP unreachable on GUI
• SSH working fine

Cause

The tomcat, httpd, restjavad or restnoded processes might become unresponsive and stop working. (Usually tomcat or httpd).

Recommended Actions

Restart the aforementioned processes with this command:

bigstart restart restjavad restnoded httpd tomcat

Note: this is not traffic-impacting.


Also you can Check in bash mode if any memory or cpu issue , check the processes

top
or

htop

Also check the following logs for any errors an share your inputs

tail -f /var/log/httpd/httpd_errors

grep -i "error" /var/log/httpd/httpd_errors

cat /etc/httpd/conf/httpd.conf | grep -i "ajp"

is it VE or f5 hardware appliance?

if it is VE, disable memory baloon / dynamic memory in the vm settings.