ConversationNotFound error

[ShadyManu94]

Hello everyone!
We are using a the toolkit for a notification bot in a prod environment, but all of a sudden, three days ago (after months that was working well), I'm receiving ConversationNotFound error when triggering the endpoint with postman.
Any idea when this error get launched?
We are using a BlobStorage as storage (which is basically like this sample), here are some pieces simplified of code (very similar to the template):

    const messageText = req.body.text;
    const email = req.body.email;

    const member = await notificationApp.notification.findMember(
      async (m) => m.account.email === email
    );

    if (!member) {
      res.status(404);
      res.json({ error: `Member ${email} not found` });
      return;
    }

    if (type === "message"){
      await member.sendMessage(messageText);
    }

without changing anything, without any edit, all of a sudden some users get ConversationNotFound, meanwhile some others work fine.. the files inside the storage are 'crypted' so I don't have a way to see if those files (around 50) contains the email I'm searching for.. When does this ConversationNotFound error gets launched?

I saw there was another similar topic in the past in this github: #8759

I tried with the method the guy said it was working:
const target of await bot.notification.installations()
and the not deprecated one
const target of await bot.notification.getPagedInstallations()

I tried to SearchScope Filter for person (even if the bot is not installed in any chat or channel, just person)
We tried to uninstall the bot from the chat, add it again and try again to trigger that email with postman, same result

Any idea?

PS: I want to add that this is unrelated to my previous post. Meanwhile I was working to make changes to that bot introducing Redis and trying to make it faster (working in local and in a completely different environment than production), that error happened to the bot which was working in prod environment.