all i can say
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I think I know the reason, Ark on Cryptopia have been depleted! Last time I checked they have less than 20k on their main wallet. I have been buying and withdraws Ark tens of thousands from there for staking and earn easy money for my Ark. I think they need more people to deposits and leave their Ark there so they could have more activities. I think I have sucked most of the Ark from there. Just my thought.
The reason is I'm selling other coins which only listed on Cryptopia, it is convenient for me to buy/sucked most of the Ark on Cryptopia.
Edit, never mind about this replied. Cryptopia main wallet have 280k Ark now. I don't know the reason why withdrawal is down oftens.