Hello JF,
if that is the case, means that somewhere along the way there is MTU lower than 1500 that is default for TRB mobile connection (and mostly all our devices), And even if you can override default value by editing network configuration, you would still need to figure out what value to set it to, since you would not want to "overkill" yours own MTU since it will affect yours connection, and for that you will need to contact yours Mobile Service Provider, actually they might be able to fix that for you from their side.
Best regards,
VidasKac