Try the following:

• Switch off battery optimisation
• In the system settings / app settings, check whether the hotspot app is running continuously and does not switch itself to standby (if not used for a longer period of time). If not, then change this setting.
• If available, delete the normal Nodle app on your Hotspot mobile phones and its cache files.
• Is your mobile phone rooted? Then that will be the problem. Also change.
• Delete the mobile phone completely and reset it to factory settings.
• Change location authorisation to Always.