Warning: Time went backwards

[ndehio]

When running the simulation, sometimes the warning "Time went backwards by -..." is printed.
What does that mean and how do I solve this issue?

Here the output of my shell:
1037.999 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -0.999 seconds! (1037999000000 --> 1037000000000)
1652.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (1652000000000 --> 1651000000000)
1719.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (1719000000000 --> 1718000000000)
2110.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (2110000000000 --> 2109000000000)
2189.999 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -0.999 seconds! (2189999000000 --> 2189000000000)
4623.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (4623000000000 --> 4622000000000)
5403.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (5403000000000 --> 5402000000000)
5445.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (5445000000000 --> 5444000000000)
6965.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (6965000000000 --> 6964000000000)
7129.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (7129000000000 --> 7128000000000)
7198.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (7198000000000 --> 7197000000000)
7889.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (7889000000000 --> 7888000000000)
9844.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (9844000000000 --> 9843000000000)
10763.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (10763000000000 --> 10762000000000)
11583.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (11583000000000 --> 11582000000000)
11649.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (11649000000000 --> 11648000000000)
12289.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (12289000000000 --> 12288000000000)
12981.000 [ Warning][GazeboDeployerModelPlugin::gazeboUpdate] Time went backwards by -1 seconds! (12981000000000 --> 12980000000000)