Subscriber management has been redesigned from junOS 15.1R3 onwards enhancing scale, performace and to support higher cps(call per second) subscriber login rate.
In a dual routing engine setup, after upgrading from previous builds such as Junos 12.3, 13.3, 14.1x50 or on a fresh install of the Junos Subscriber Management build, the system must be rebooted. Refer to Configuring Junos OS Enhanced Subscriber Management.
For initial setup, operators normally follow Juniper's tech document, Configuring Junos OS Enhanced Subscriber Management. However in dual routing-engine setup, due to certain misconceptions, operators may not follow the complete procedure in order for the router to enable Enhanced Subscriber Management features and this can cause router to be unstable. May I know what was the exact junos version in 15.1 branch?
As i mentioned earlier, NOT all junOS version are quailfied for subscribers-mgmt used. Since you're currently non quailfied subscriber-mgmg build, i would recommend that you reach out to local juniper accounts team to evaluate your current subscriber related config and suggest JunOS version accordingly.
Following are subscribers-mgmt quailfied:
JUNOS 15.1R4 onwards: (15.1R5, 15.1R6, 15.1R7)
JUNOS 16.1R4 onwards: (16.1R5, 16.1R6, 16.1R7)
If you ask me or JTAC (me again), I would recommend following JUNOS for subscribers-mgmt use:
JUNOS: 16.1R7, 17.3R3, 17.4.R2
Note1: 15.1 branch is going be EoL soon.
Note2: Use the latest SR JunOS of an mainstream branch cause its includes the most recent bug fixes.
Coming back to the orginal post, its known bug condition that i've explained in previous posts.
Those logs are not harmful and you can filter them using KB9382 or resolve by means of S/w upgrade.