Trying to stab here since the only clue I have is "from Japan" but maybe the connection is routed in Russia instead of routing via Asia/ME or US/CA/UK (more lik

Trying to stab here since the only clue I have is "from Japan" but maybe the connection is routed in Russia instead of routing via Asia/ME or US/CA/UK (more likely if the connection is from KDDI/au than NTT) and your Hetzner instance is in Finland. There are relatively few links from Japan to Russia (note that they are carrier links so they are unhampered by censoring) so connections are impacted that way. Maybe run a traceroute to check it, and then ask Hetzner and your ISP (be patient on your ISP, but sometimes you tend to be lucky) to fix this issue. Unfortunately short of running a VPN to a different uplink (Scaleway! OVH! The horror!) or switching to a different ISP with different uplink, there's nothing you can do about this.