Value NaN in alert message but ok in plot and lable as script

Hi,
I have a function to calculate leverage
I have a function in Pinescript that returns a value based on several indicators:

    varip a = 0.0
calculate_() =>
    period = 50
    basis = ta.sma(src, period)
    dev = mult * ta.stdev(src, period)
    upper = basis + dev
    lower = basis - dev
    nATR = ta.atr(period) / src
    hATR = ta.highest(nATR, period)
    lATR = ta.lowest(nATR, period)
    nSD = ta.stdev(src, period) / src
    hSD = ta.highest(nSD, period)
    lSD = ta.lowest(nSD, period)
    MA = ta.wma(nATR, period)
    perm = 100 * math.abs(nATR - MA) / MA
    pers = 100 * (nSD - lSD) / (hSD - lSD)
    pera = 100 * (nATR - lATR) / (hATR - lATR)
    perb = 100 * (src - lower)/(upper - lower)
    per = gear == 4 or gear == 5 ? (perm + pers + pera + perb) / 4 : gear==1 ? math.min(100 , (pers + pera + perb) / 2.5) : (pers + pera + perb) / 3
    EL = (100 - per) / (6-gear)
    float(math.max(1,int(EL + .5)))

a:= calculate_Leverage()

plot(a, 'Leverage')
label.new(bar_index, high, str.tostring(a))

It plots and labels the right value.

But when I try to put it in an alert message, I get only NaN on my alert. Tried both ways and same result:

var msgLongBuy = str.format("{0,number,#.#}", a)
str.tostring(a,"#.00)")

Any idea why?

Value NaN in alert message but ok in plot and lable as script

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