After upgrade ispConfig: www. does not always work as expected

When a user enters the domain name in the address bar of the web browser, the website shows.
When a user enters the domain with www. before the domain name, the website does not show and gives a database connection error. Most probably the user is being served something else (most probably another domain with a database error).

Not sure how to troubleshoot this. Any suggestions?

I will look trough the log files later (this evening) and see what I can find there.

 

1. Yes. The setting "Auto-Subdomain" is set to "www".
2. No, there is a CNAME record in place: "www" points via CNAME to the domain name itself.

Code:

$ dig a www.frieslanddeuren.nl

; <<>> DiG 9.16.13-Debian <<>> a www.frieslanddeuren.nl
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10416
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.frieslanddeuren.nl.        IN    A

;; ANSWER SECTION:
www.frieslanddeuren.nl.    2809    IN    CNAME    frieslanddeuren.nl.
frieslanddeuren.nl.    2797    IN    A    136.144.206.44

;; Query time: 0 msec
;; SERVER: 172.16.0.254#53(172.16.0.254)
;; WHEN: do apr 15 16:05:19 CEST 2021
;; MSG SIZE  rcvd: 81

 

Yes, it does. It works for me, but some visitors complain. I did test this with another browser and for me this works absolutely fine. I guess it's a problem on their end but I am not sure yet. I think I might contact one of them and just check what's going on via TeamViewer or something like that. It's a bit odd.

 

This has been resolved too. I figured this out by executing "tail -f other_vhosts_access.log" in console and parallel to that visiting the website - hitting F5 several times. I did notice another website was being queried (aha). What I did first is to switch off the website and switch in on again. That didn't help, so next I did open the web domain settings of the other website in ISPConfig. Low and behold: the IPv6 address was selected. After removing the IPv6 everything works like a charm.