Hello LAZORRA
It seems your WLAN-Stick is not fully supported as an AccesPoint. For an rpi also it is not stable to use the internal wifi as WLAN-Client and make an own AccesPort simultan. After installing an little WLAN-Router onboard and use it only as Client, my Preformance was much better with no Errors or Offline Periods. These LTE-Routers got really cheap (€50-60), often you get them together with an monthly LTE unlimited Plan here in Europe for under 15€.
Otherwise try an updated Driver for your USB-Adapter with better AP Support. But be warned, an little external Router will save you much Trouble and Delays - acting as AP-Router your pi3 will slow down. And most Routers are also capable to do Firewalling and 5G for free and all Boat-Devices have an stable Internet even if your Pi is rebooting.
Good Luck - Holger
PS: found an URL abot the various USB-WLAN Adaptors: https://elinux.org/RPi_USB_Wi-Fi_Adapters
It seems your WLAN-Stick is not fully supported as an AccesPoint. For an rpi also it is not stable to use the internal wifi as WLAN-Client and make an own AccesPort simultan. After installing an little WLAN-Router onboard and use it only as Client, my Preformance was much better with no Errors or Offline Periods. These LTE-Routers got really cheap (€50-60), often you get them together with an monthly LTE unlimited Plan here in Europe for under 15€.
Otherwise try an updated Driver for your USB-Adapter with better AP Support. But be warned, an little external Router will save you much Trouble and Delays - acting as AP-Router your pi3 will slow down. And most Routers are also capable to do Firewalling and 5G for free and all Boat-Devices have an stable Internet even if your Pi is rebooting.
Good Luck - Holger
PS: found an URL abot the various USB-WLAN Adaptors: https://elinux.org/RPi_USB_Wi-Fi_Adapters