AWS lightsail - how can I troubleshoot/resolve DNS propogation problem

Set up the DNS zone (A record, MX record & TXT records) but for whatever reason/s it still doesn't want to resolve. Now having problem getting to the vm using the IP address. Been over the DNS zone settings numerous times and I'm certain they're fine. What's also weird is that if I try the domain name on my phone it'll work once but when I try moments later on a desktop the browser just sits there. Is there anything in the lightsail control panel (under the Networking header) where we can troubleshoot DNS problems? When I check the A record at www.whatsmydns.net it looks good, mostly green check marks with a few red Xs but the red Xs are outside the US. Has anyone had DNS problems recently & how did you work through them. All feedback is welcome