Hi there! I understand that your Nextplus app is logging you out unexpectedly and then it's not letting you log back in, even though you've tried multiple times. That must be inconvenient. To help you better, could you tell me if you get any specific error messages when trying to log back in? Also, have you noticed if this happens when switching networks or after an app update?

Meanwhile, let's try some steps to troubleshoot:

1. Check your internet connection: Make sure your iPhone is connected to a stable Wi-Fi or cellular network.

2. Force close and reopen the app: Sometimes closing the app completely and restarting it can clear temporary glitches.

3. Clear app cache/data (reinstalling the app on iPhone):
- Delete the Nextplus app from your device.
- Restart your iPhone.
- Reinstall Nextplus from the App Store.
- Try logging in again.

4. Reset your password: If the app says your account doesn't exist or refuses to log in, try using the "Forgot Password" option to reset your password by email. This will also confirm if your account is still active.

5. Check for iOS updates: You mentioned you are on iOS 18.3.1, so you are on the latest version, which is good.

6. Check for Nextplus server status: Sometimes login issues occur due to server problems. You can check app status via social media or community forums.

If you have already tried these steps or if the issue persists after this, please let me know. We might need to look deeper into account issues or check for app-specific bugs.

Are you able to try these steps and tell me what happens?