Assuming UM436 through Namibia ?
If so the AIRAC cruise table record looks incorrect as it should be 'SA' and not 'SO' to assign even flight levels as per the AIP.
Workaround, assign an appropriate level from ATUPI ( establish an initial cruise on first compute )
I apologize, I had not received the notifications of the replies and therefore I had not noticed them. I deactivated the weather (in fact it had expired) and now it seems to work correctly. thank you very much