I saw this issue corrected later today and advised VULTR in case they knew of something that had changed. While testing earlier with them their test of
dig -x x.x.x.x @1.1.1.1 (x.x.x.x = my instance IP) resulted in a Answer record for PTR while mine didn’t.
They reply to my update saying they had been made aware of an issue with their DNS earlier today (I assume me) and corrected it. So I guess it’s worth contacting the host (as the MaiB message advises) just in case there’s something a miss on their end. Just wanted to update this topic for other to see this outcome.