Using 1.28 - build 122 on an RT-AC68U, the bandwidth monitoring for daily, weekly and monthly and similar IP monitoring options (daily, monthly) report 0 bytes usage.
Same results occurred under builds 120 and 121.
Various media were tested (RAM, NVRAM, CIFS, and custom path to local USB storage under /tmp/mnt/EXTERNAL/).
Files are created; data is empty. NVRAM wipe was done multiple times, no change.
Problem is reported by dozens of users via forums; only seems to affect the AC68U.
NOTE the real-time and 24-hour displays work fine.