Samples timestamp jumps back to internal time

[amir-zviran]

Describe the bug
I'm using the 3DM-CV7, outputting data at 200Hz. It is connected to a PPS signal generated by a GPS device, and I'm sending it a time reference on the /ext/time topic every 1 second, around 0.2s from the beginning of the second.
Everything is working great most of the time - I look at the samples and they are time-synced with the GPS as expected.
Nevertheless, in some rare cases that I still haven't found a way to reproduce, the samples timestamp jumps back to the "internal time", which seems to be the time from power up + 315964800s. The timestamps stay behind for less than 2 seconds, till they return to the GPS time at the beginning of the next full second.

For example I see this series of timestamps:

1740564858045000076 (2025-02-26 12:14:18.045) 
315965245050000011 (1980-01-06 2:07:25.050)
...
315965246995000004 (1980-01-06 2:07:26.995)
1740564860000000000 (2025-02-26 12:14:20.000)

To Reproduce
I haven't found a way to reproduce. It happened to me two times in the last few weeks.

Expected behavior
The samples timestamps should always follow the GPS time.

Environment (please complete the following information):

• OS: Ubuntu 20.04
• Architecture: arm64 (Jetson Orin-AGX)
• ROS Version: noetic
• Version: 4.5.0
• Sensor(s): 3DM-CV7

Modifications
I'm using the time_sync_status branch.

Launch Parameters

# ******************************************************************
# General Settings
# ******************************************************************
port : "/dev/ttyACM0"
baudrate : 921600
set_baud : True

timestamp_source: 1

# ******************************************************************
# Frame ID Settings
# ******************************************************************
use_enu_frame : False

# ******************************************************************
# Kalman Filter Settings (only applicable for devices with a Kalman Filter)
# ******************************************************************
filter_enable_gnss_pos_vel_aiding     : False
filter_enable_gnss_heading_aiding     : False

filter_pps_source : 3

filter_declination_source : 1

# ******************************************************************
# Other Device Settings
# ******************************************************************
gpio_config    : True

gpio1_feature  : 2
gpio1_behavior : 1
gpio1_pin_mode : 0

# ******************************************************************
# Publisher Settings
# ******************************************************************
imu_data_raw_rate : 0
imu_data_rate : 200
imu_mag_data_rate : 200

filter_human_readable_status_data_rate : 0
filter_imu_data_rate : 200

mip_system_time_sync_status_data_rate : 1

# External aiding measurement configuration
subscribe_ext_time : True

Additional context
Add any other context about the problem here.