IMEI Number status is unknown AUXUS NOTE 5.5 I have changed my SIM from my another Android phone (which was Lava X1) to Auxus Note 5.5. As soon as I changed and rebooted phone, it got locked.

I understood that it was due to Mobile antitheft apps was been install in the Lava X1.

Now I restored Firmware with help of service support but its IMEI number has been lost and I am not able to restore it.  Is there any solution?
According to my experiences, 

you just need the Region Rom for your Operator and Country and flash the Modem in your phone.and of course, if you have any backup of Efs, just restore or flash it.

also, try to download stock rom for your region and then test it.

hope this fixed. else, 

maybe you need the BoX for fix this.