Hi Awijit,
the error in in the arcotwebfort.log:
05/18/18 14:46:05.775 INFO RADIUS 00004032 00659325 - [UDS] UDS Log : Successfully retrieved the user [RGIUPPA] for organization [GBI]
05/18/18 14:46:05.775 INFO RADIUS 00004032 00659325 - Transaction processing(internal-pre) is about to start.
05/18/18 14:46:05.775 INFO RADIUS 00004032 00659325 - Transaction processing(internal-pre) is complete.
05/18/18 14:46:05.775 INFO RADIUS 00004032 00659325 - Transaction processing(proc) is about to start.
05/18/18 14:46:05.775 INFO RADIUS 00004032 00659325 - HandleTOTP::ReferenceCounter : 50888248, Auth Window: [50888247, 50888258], Sync Window : [50887249, 50889248]
05/18/18 14:46:05.791 INFO RADIUS 00004032 00659325 - VerifyOTP Result : INVALID_OTP
It seems that when the enduser if offsite the ca mobile otp went out of synch.