I transferred GRIN between exchanges. From Hotbit to Kucoin. Status on HOTBIT is complete. I have txid, and the transaction is not confirmed and did not come to Kucoin. What to do ? 
Contact Hotbit support. They are creating transactions with zero fee. It looks like that doesn’t work any longer.
Hey man just read your problem,
I have something similar from bibox.
please check my post.
They also used null for transaction fee.
Did you solve your issue by the way.
check my post. Similar issue with different exchanges.
Hotbit credited my account with the amount of grin that got stuck. I then could make two succesful withdrawals. Still no transaction fee but Hotbit got lucky this time.
I have no idea why exchanges would gamble with the fee like this. Hotbit as a fee of 0.3 grin. Plenty to pay a miner fee.