Invalid transaction when `session.newSession` is emitted

[luispdm]

Hi, Laos developer here. There's something I want to share here that you might be unaware of.

We've been investigating an issue in our parachain that causes transactions to be invalid occasionally. This happens when session.newSession is emitted.

The issue comes from this line of pallet-session: https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/session/src/lib.rs#L563. It's been reported in the polkadot-sdk repo paritytech/polkadot-sdk#184 but it remains unresolved as of today.

We successfully reproduced the issue in your runtime using Chopsticks with the following modified configuration:

endpoint: wss://kilt.ibp.network/
mock-signature-host: true
db: ./kilt.db.sqlite
runtime-log-level: 5
port: 9999

import-storage:
  System:
    Account:
      - - - 5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY
        - providers: 1
          data:
            free: 1000000000000000
  ParachainStaking:
    Round:
      Current: 12640
      First: 7583016
      Length: 3

We've reduced the round length for testing purposes. For reference, this is the screenshot of the invalid transaction:

And this is the screenshot of the newly produced block:

As you can see, system.remark is not emitted.

This is the issue on our side, in case you want to keep track of it.

Thank you for your time.

[ntn-x2]

Thanks for the issue. We will be monitoring it!