As in any other game, bugs or issues can affect game play. Issues can arise after an update to the game, but can also appear randomly.
It is important that these errors are reported so the developers can take care of them as fast as possible.
You can create a bug report by going to Help > Bug Reports > Create new bug report, or by following this direct link.
This will take you to the page where you can create the report.
It is important that you describe the issue in as much detail as possible. It will help if you say exactly what you did when the issue appeared, and what happened in the run up to it. If it is a graphical bug, then you should if possible include a screenshot.
Any and all tips and tricks to help reproduce it, will help.
Issues need to be reported and must not be taken advantages of as that would be against the game rules.