Domain resolves fine on other ISPs and in Google DNS (126.96.36.199) however there's this one ISP that suddenly is having issues on a server where we host our domains.
When I gave them some sample domains, they were able to fix it but the rest of the domains that I didn't mention still wasn't resolving. So I think they only did a "manual" bandaid fix (maybe kinda like manually editing the IPs in your Windows hosts file, not sure, hopefully not).
I want to them fix the issue properly. I'm not sure what's going on their end but it gives me the impression they are clueless about the real cause of the problem since the other domains that I didn't mention are not resolving.
Ideally, what troubleshooting steps should they take on their end to properly fix the issue?