The good news is that Apple is aware of the problem, and says that it affects only a small number, about 10%, of iMessage users. Apple did say that it will fix the problem with an upcoming iOS update. No date was given as to when iPhone users can expect to receive this update. Apple's status board still shows no issues with iMessage even though the Cupertino based tech titan has admitted the problem.
While waiting for the update to come, iPhone users can try to fix the problem by turning their phone off and on, or by going into the settings, turning off iMessage. To do so, go to Settings > Messages. Next, reset networking settings in Settings > General > Reset. Finally, re-enable iMessage in Settings > Messages.