Problem to attach to 3G during on DL Only from 4G

Mobility
1

Dear Èxperts,
On field testing, having problem to attach to 3G during on DL Only from 4G.
Coverage is Excellent.
Any suggestion?

2

Check layer 3 messages.
What is the reason in attach? Reject or location area update failure?
Those are NAS messages but should be available in DT logs.

3

Do You mean SRVCC not happening?