It sounds like you're running your own VPS webserver...
If you SSH to your server, you can do nslookup and also see what /etc/resolv.conf are showing.
Here's my results # nslookup www.temis.nl
Server: 208.67.222.222
Address: 208.67.222.222#53
Non-authoritative answer:
www.temis.nl canonical name = temis.pmc.knmi.cloud.
Name: temis.pmc.knmi.cloud
Address: 34.248.63.123
Name: temis.pmc.knmi.cloud
Address: 52.214.85.242
Name: temis.pmc.knmi.cloud
Address: 63.32.9.176
# cat /etc/resolv.conf
; generated by /usr/sbin/dhclient-script
#nameserver 8.8.8.8
nameserver 208.67.222.222
nameserver 1.1.1.1
nameserver 212.227.123.16
nameserver 212.227.123.17
#
If you have a caching DNS on your server, then try restarting it. If your upstream nameserver entries point to your hosters caching DNS servers, put the common external ones like I did before them in /etc/resolv.conf
I've found that the default DNS servers with hosters tend to have more resolution issues than the well-known public DNS resolvers.