I'm not sure when it started but at least for the last couple of days I see in ipv6 gateway monitoring:
RTT: 191.5 ms
RTTd: 123.9 ms
Loss: 3.0 %RTT used to be 15-25 ms and RTTd around 10 ms.
gif interface has same MTU as is on tunnel broker's side: 1480. gif MSS is also set as 1480 and system automatically subtracts 60b and reaches 1420. It is checked by http://pmtud.enslaves.us :
Direction
| Maximum Size Segment | Client Sent MSS | Notes |
| Server to Client IPv4 | 1460 | 1460 | OK |
| Client to Server IPv4 | unlimited | n/a | OK |
| Server to Client IPv6 | 1420 | 1420 | OK |
| Client to Server IPv6 | unlimited | n/a | OK |
So, is it something related to opnsense (latest 25.7.11) or more on HE tunnel broker's side?