What could cause IRAT preparation failures to unknown target RNC on a site?

Hi guys, i am observing IRAT preparation failures due to Unknown target RNC on one site. IRAT preparation failures are with co-located 2G cells and one neighbor site.
I have checked nbr definitions in 3G dump, its ok no issue observed. Whats else could be the reason?

Vendor is ZTE

Target RNC or BSC? 2G frequencies are clean? BSIC verification is on?

I had irat preparation fail 3g to 2g for two 2g cells; Reason was wrong MNC, normally mcc-mnc 286-02; there were write 286-002. You should Check inconsistency for Target cells

Yes that’s true

Cause is unknown target RNC. 2g freq are clean, BSIC is also ok

Check on external definition of 2g cells on Rnc, this defination have ci, basic, bsc, bcch, lac of the target 2g cells

Already done no issue observed. All definitions are ok

Hmmm, great will check this, Today deleted & added relations again. Will observe tomorrow.

Is there congestion in 2g site?

Yes there is, but if its due to 2g cell congestion then the failure cause would be different like “fails due to physical channel”

U might check cell definition on CN… This as well might cause interrat problems

Ok we also think this because every 3g cell is degraded with that 2g site

Check LK license at RNC… this will resolve the Unknown target RNC