If the SDCCH MHT has increased, then the SDCCH traffic must have increased as well !
Traffic = MHT * SDCCH_Attempts
So unless the overall number of SDCCH_Attempts have decreased, it doesn’t make sense to me.
If attempts have decreased, then something must have occurred ! (for example : less IRAT HO 4G-2G or 3G-2G, or fast reselection to UTRAN/LTE)
You may consider checking the cause of SDCCH establishments (MOC, MTC, LAU, SMS, IRAT reselection, etc) thanks to RAN counters. This may point you to the right direction.
BR / Pix