Porter loses carbonation when chilled

I made a porter using the Beer Smith app which is pretty much a standard porter recipe. I used 6 oz of cane for a 5 gal batch. I aged it for a month. It’s pretty carbonated at room temp, but when I chill it it looses it carb. It tastes great but lacks the fizzle. Any suggestions?

Sorry all, I did use corn sugar. It’s all I use. This is the only batch that lost carbonation when chilled.

How did you prime it,  and with what type and quantity of priming sugars?

Why cane sugar??  Why not XLDME? And how much volume in cups is 6oz?  Remember the formula is 3/4 cup per 5 gal.

Because cane sugar is WAY cheaper and does the same thing

To the OP , how many bottles have you tried?
Beer will lose SOME of its carbonation when really cold but if its carbed at room temp its carbed at 35

OH! you may have hit it right there. Could there have been a weight vs volume error here?

White Sugar (Granulated)

Cups         Grams       Ounces
2 Tbsp   25 g        .89 oz
1/4 cup   50 g        1.78 oz
1/3 cup   67 g        2.37 oz
1/2 cup 100 g        3.55 oz
2/3 cup 134 g        4.73 oz
3/4 cup 150 g        5.3 oz
1 cup     201 g        7.1 oz

As Babalu87 says: cane sugar (any sugar) does the same thing, and actually works better because the yeast find it easier to consume giving more predictable results.

As far as the OP having carbonation at room temp but not fridge temps, I’d give it another weak or two and try it again. The reason why it seams more carbbed at room temps is because the cold temps can hold more Co2 in suspension so it will foam less when cold.