We are seeing bug CSCsx21595:
Losing ntp source lookback config
Losing the config after reload/upgrade to 124(23.15)T2
Manually readd the config back
We are running c2800nm-advsecurityk9-mz.124-24.T1.bin on our 2811 router.
We can't see 12.(24.6)T1 on Cisco Systems which is supposed to address the above bug: