I'm having this event and I'm not sure what are the conditions required to trigger it, also what does it mean exactly since the documentation does not say more than a line about it.
See this tutorial on the timeslot API. NRF_EVT_RADIO_SIGNAL_CALLBACK_INVALID_RETURN means that the return value for the radio callback which is passed in sd_radio_session_open(radio_callback) is invalid. The return value should be of type nrf_radio_signal_callback_return_param_t.
In the tutorial they recommend to assert, but I'm looking for a way to keep my application running without a problem after I receive this kind of event. In this case what do you recomend to do? (restart timeslot, ignore the event, finish timeslot and request another one). Than you for your help.
You should change the radio callback to return the correct type. I don't know what will happen if you continue the application. The tutorial says that you should assert because you should fix the code in the radio callback such that this error never happens.