It's my 2nd loan after the first fully paid loan, is it necessary to signed message again?
Yes, it is.
You must sign a message with a staked address (or any address that you've publicly posted in the past) stating that you are taking a loan from me with the date.
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7. A signed message is required for a no collateral loan.
I used the same btc address in the first loan.
It's meant for security purposes, and to prevent impersonation. I just checked your trust page and no recent password or email changes, but that still can't guarantee you weren't compromised, Moreover, It only cost as much as posting a reply here to sign a message, Of which imo shouldn't be optional at least not for a sum of about $300.