More importantly. Somehow in this turn Vecna lost a reaction. During Leon's turn you said Vecna has one reaction remaining, when he has two after that. And I would not have used one in response to Malek.
Here is a complete list of Vecna's uses of reactions and legendary resistances (I think I missed LR someplace though...)
Round 1:
On Malek's turn, Vecna used Fell Rebuke (1 reaction).
On Hjalman's turn, Vecna used Fell Rebuke (2 reactions).
On Egar's turn, Vecna uses Legendary Resistance (1).
VECNA'S turn, reactions refresh.
On Leon's turn, Vecna does nothing.
Round 2:
On Malek's turn, Vecna used Fell Rebuke (1 reaction).
On Hjalman's turn, Vecna uses Legendary Resistance (2).
On Egar's turn, Vecna used Fell Rebuke (2 reactions).
VECNA'S turn, reactions refresh. VECNA uses Dread Counterspell (1 reaction). (This is probably what you are missing because he had to use it in response to my having Egar use
shield against the attacks by Afterthought.)
On Leon's turn, Vecna used Fell Rebuke (2 reactions).
Round 3:
On Malek's turn, Vecna used Fell Rebuke (3 reactions).
On Hjalman's turn, Vecna no longer can use reactions.
On Egar's turn, Vecna does nothing.
Currently VECNA's turn...