On 27 Apr 2021, Flavio Bessa said the following...
 
 FB> Hello folks, 
 FB> 
 FB> I have messed up my nodelist here and now every Fido address has 3
 FB> different entries.
 FB> 
 FB> How do I delete the current nodelist database on Mystic? Need to start
 FB> over... 

I had the same thing happen due to not pointing to the correct nodelists in
the mutil.ini file in the nodelist section. 

I think the nodelist.txt is in the mystic\data directory. I had to replace it
with a raw fidonet node list (nodelist.###) and then merging worked again.
--- Mystic BBS v1.12 A46 2020/08/26 (Windows/64)