The only issue we’ve had with Vultr was actually an AT&T issue. They had (maybe still have) a problem with one of their routers that passed traffic to PCCW which is a major peering partner for Vultr, and it resulted in major packet loss. Vultr eventually dropped PCCW from their blend for their west coast datacenters because they couldn’t figure it out.
Besides that, no network issues I’ve experienced with them. @dobrosavljevic is right, use mtr to troubleshoot network issues. There is a post that discusses the best way to do this already - https://community.freepbx.org/t/linux-nerds-how-to-pinpoint-where-the-network-problem-is/76853/2?u=adell4444