This bug was fixed.
My Sim wanted to remarry after their partner’s death. Unfortunately that is not possible since they are still married to their dead partner.
The game doesn’t resolve the relationship to the dead Sim correctly.
First you need the ID of both your Sims (repeat for each Sim)
- sims.get_sim_id_by_name <Firstname> <Lastname>
Then you can destroy the relationship
- relationship.destroy <ID Sim 1> <ID Sim2>