Offline signing. Sometimes signature fails

[apeTim]

Problem

Hello everyone. I am doing offline transaction signing with solana web3.js. The Problem is that sometimes this functions executes normally and txhash prints to the stdout, but sometimes it throws an error:
Error: Signature verification failed, however, im not changing the code, just running it in the different time.

For me, it is really weird. Would appreciate any help on this issue 🙏

Code to reproduce

import { clusterApiUrl, Connection, Keypair, LAMPORTS_PER_SOL, Message, NonceAccount, NONCE_ACCOUNT_LENGTH, SystemProgram, Transaction } from "@solana/web3.js"
import * as k1 from './k1.json'
import * as k2 from './k2.json'
import * as Base58 from 'base-58'

const connection = new Connection(clusterApiUrl('devnet'))

const sender = Keypair.fromSecretKey(Uint8Array.from(k1))
const receiver = Keypair.fromSecretKey(Uint8Array.from(k2))

const amount = 0.01

const INSTRUCTION = SystemProgram.transfer({
    fromPubkey: sender.publicKey,
    toPubkey: receiver.publicKey,
    lamports: amount * LAMPORTS_PER_SOL
})

const getTxSignature = async (signer: Keypair, instruction: SystemProgram, blockhash: string) => {
    const tx = new Transaction()
    tx.add(INSTRUCTION)

    tx.recentBlockhash = blockhash
    tx.feePayer = receiver.publicKey
    tx.sign(signer)

    const signature = tx.signatures.find(signature => signature.publicKey.toBase58() === signer.publicKey.toBase58())

    return signature
}

const send = async () => {
    // get recent blockhash
    const blockhash = (await connection.getRecentBlockhash()).blockhash
    // getting signatures
    const senderSignature = await getTxSignature(sender, INSTRUCTION, blockhash)
    const receiverSignature = await getTxSignature(receiver, INSTRUCTION, blockhash)

    const tx = new Transaction().add(INSTRUCTION)
    tx.recentBlockhash = (await connection.getRecentBlockhash()).blockhash
    tx.feePayer = receiver.publicKey

    tx.addSignature(senderSignature.publicKey, senderSignature.signature)
    tx.addSignature(receiverSignature.publicKey, receiverSignature.signature)

    console.log(`txhash: ${await connection.sendRawTransaction(tx.serialize())}`);
}

send()

[t-nelson]

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