I noticed something odd about Avicebron a month ago
but it wasn’t until yesterday that I compared the NA and JP servers.
Perhaps this is already well known but his behaviour isn’t consistent on the two servers , the big difference is how his third skill works.
On NA the Invincibility counts down before enemy action but on JP it does that after.
In effect right now on NA it only provides a benefit for 2 turns and for the final turn it will just give a false sense of security as the buff will expire before the enemy acts.
In general this problem might not occur often but I’ve managed to trigger it a couple of times unintentionally.
For example I’ve had this problem during semi-solo with Avicebron (PG), x, Georgios when I rushed with my alt.
I’m speaking from personal experience that it is possible that the solo servant could eat an NP that you believed the buff would soak.
This has happend on two different phones and accounts so it doesn’t feel like an isolated incident.
I’ve shared my findings with FGO support so hopefully this will be solved.
Edit: After @Justsomeguypassingby identified some of the faulty conclusions I had drawn, I did another test with equal base conditions.
It is only when Chen Gong is used to kill Avicebron that the skill behaves differently.
On both NA and JP the Invincibility buff lasts 3 turns HOWEVER the remaining stacks will remain for an additional player phase.
As such be aware that it might prevent some defensive measures such as Merlin’s Illusion from being used on turn 4.