Recalled these threads [1 | 2] pertinent to some IPv6 connectivity issues between a FB and a TO.
[1] IPv6: Ask for help: No re-connect to v6 - #18 by anon50890781 - SW help - Turris forum
[2] IPv6 Issue cascade (Fritzbox --> TurrisOmnia) - #3 by ib54003 - SW help - Turris forum