GL-MT300N-V2 random stop answer through OpenVPN

Hello, I have a GL-MT300N-V2 configured as explained in this thread (I post also a summary image to show the actual configuration):

The system works correctly, the GL-iNet connect to the VPN server, it allows the navigation to the LAN connected device through WAN, VPN, and LAN. Also through WiFi, I can access to the GL-iNet interface to it’s IP and to the LAN connected devices typing
I’m also able to open the LAN device interface directly from the OpenVPN server.

The problem is that randomly, the GL-iNet become not available through the OpenVPN direct IP access (when I type on the browser the GL-iNET OpenVPN IP address or if I try to connect through ssh to the OpenVPN IP address).
The GL-iNet remains unavailable for a couple of minutes.
If I try to connect to the LAN device from the OpenVPN server, the connection will be unlocked and I can connect again typing the GL-iNet OpenVPN IP address.

Any suggestion, please?