I am having CSFB issues. The CSFB trigger seems to be ok, as the UE is correctly redirected to the right frequency. After it finds the right UMTS cell, it performs a registration process, and finally, when the LAU procedure ends. the IU is released and the call does not proceed.
The MSC are pooling MSC, and in this cases the UE is on a LAC border so no possibility of changing the TAC LAC mapping. Meaning no MTRF is needed and no chance of changing the TAC/LAC.