I made no changes on the I2P side.
Dunno why it happens.

In the ergo config:
# account options
accounts:
# is account authentication enabled, i.e., can users log into existing accounts?
authentication-enabled: true

# account registration
registration:
# can users register new accounts for themselves? if this is false, operators with
# the `accreg` capability can still create accounts with `/NICKSERV SAREGISTER`
enabled: true

# can users use the REGISTER command to register before fully connecting?
allow-before-connect: true
...
# enable login to accounts via the PASS command, e.g., PASS account:password
# this is useful for compatibility with old clients that don't support SASL
login-via-pass-command: true

# require-sasl controls whether clients are required to have accounts
# (and sign into them using SASL) to connect to the server
require-sasl:
# if this is enabled, all clients must authenticate with SASL while connecting.
# WARNING: for a private server, you MUST set accounts.registration.enabled
# to false as well, in order to prevent non-administrators from registering
# accounts.
enabled: true

But if you already had an account, simply add your SASL username and SASL password to the config file of your client, and then connect.