Animation only plays once? Unsure if it's a client or server problem.

Server:

--[!] SERVER
-- globals
local ROLL_SPEED = 100 -- we can change these two for the speed/amount of time we roll
local ROLL_TIME  = 1

-- private
local create = function (obj)
    obj = Instance.new(obj)
    return function (props)
        for prop, val in next, props do
            obj[prop] = val
        end
        return obj
    end
end

local isAlive = function (Player)
    local char = Player.Character
    if not char or not char:IsDescendantOf(game.Workspace) or not char:FindFirstChild "Humanoid" or char.Humanoid:GetState() == Enum.HumanoidStateType.Dead then
        return
    end
    return true
end

-- set up
local remote = create "RemoteEvent" {
    Name   = "RollRemote";
    Parent = game:GetService('ReplicatedStorage');
}

-- public
local rolling = { }
remote.OnServerEvent:connect(function (player, vec)
    if not vec or not typeof(vec) == "Vector3" or vec.magnitude > Vector3.new(1, 1, 1).magnitude then
        return -- the magnitude check here is to make sure that players aren't sending you vectors that are greater than the unit vector of their movement direction
    end
    if isAlive(player) and not rolling[player] then -- we're checking to see if they're in the 'rolling' table to ensure they're not spamming it, which would create multiple bodyvelocities
        local root, hum = player.Character:FindFirstChild 'HumanoidRootPart', player.Character:FindFirstChild 'Humanoid'
        if root and hum then
            local prevWalk = hum.WalkSpeed

            rolling[player] = true
            hum.WalkSpeed = 0 -- we can remove their walkspeed here to stop them from being able to move whilst they roll other than through their bodyvelo

            local velo = create "BodyVelocity" {
                Parent      = root;
                MaxForce = Vector3.new(1, 0, 1) * 10000;
            }
            velo.Velocity = vec * ROLL_SPEED
            delay(ROLL_TIME, function () -- after we've rolled for our preset time, we can reset everything
                if velo then
                    velo:Destroy()
                    hum.WalkSpeed = prevWalk
                end
                rolling[player] = false
            end)
        end
    end
end)

Client:

--[!] CLIENT
local Player = game.Players.LocalPlayer
repeat wait() until Player.Character
local Character = Player.Character or Player.CharacterAdded:Wait()
local Humanoid = Character:WaitForChild("Humanoid")

-- environment
local Controller   = require(Player.PlayerScripts:WaitForChild("PlayerModule")):GetControls()
local InputService = game:GetService('UserInputService')
local RollRemote   = game:GetService('ReplicatedStorage'):WaitForChild 'RollRemote'

-- variables
local Anim = Instance.new("Animation")
Anim.AnimationId = "rbxassetid://7731516813"
local animationTrack = Humanoid:WaitForChild("Animator"):LoadAnimation(Anim)

-- private
local getMoveVector = (function ()
    return Controller:GetMoveVector()
end)

local getRelativeMoveVector = (function ()
    local vec = getMoveVector()
    return game.Workspace.CurrentCamera.CFrame:inverse():VectorToObjectSpace(vec)
end)

-- init
InputService.InputBegan:connect(function (input, gameProcessed)
    if gameProcessed then
        return
    end
    if input.UserInputType == Enum.UserInputType.Keyboard then
        local key = tostring(input.KeyCode):sub(14)

        if key == "LeftControl" then
            RollRemote:FireServer(getRelativeMoveVector())
            animationTrack:Play()
        end
    end
end)