Kraken recently upgraded its software from 100% bullshit to 99.9% bullshit.

In connection with that everyone's BTC and Tether addresses (the addresses you used to send BTC or Tether to Kraken) will expire on Oct 31.

So you need to generate new ones:

How do I generate the new addresses?
The new addresses are generated in the usual way.

  1. Log into your Kraken account
  2. Navigate to Funding > Deposit > XBT (or USDT)
  3. Click “Generate New Address”