Error in mutate_impl(.data, dots) : Evaluation error: k <= n is not TRUE

i = 3
QBrollavgDT <- data.table(rankDT)
QBrollavgDT <- QBrollavgDT[, c("Player_Name", "Season", "Week", "FDP")]
#QBrollavgDT <- subset(QBrollavgDT, Player_Name == "K.Collins")                 <- This works
#QBrollavgDT <- QBrollavgDT[c(381,759,1140,1510,1888,2264.2641), ]              <- these are the rows that thorw the error

        #begin calculating the rolling average and eliminating players with < i games played

        QBrollavgDT <- setDT(QBrollavgDT)[, if (.N >= i) .SD, by = Player_Name] #this eliminates all players with < i games played
        QBrollavgDT <- QBrollavgDT %>% #this is the code that puts the rolling average on and names the column RollAvg
                arrange(Player_Name, Season, Week) %>%
                group_by(Player_Name, Season) %>%
                mutate(RollAvg = zoo::rollapply(FDP, i, mean, by = 1, align = "right", fill = NA))