What to do if you are experiencing an error or glitch in-game
Many issues can be resolved by simple trial and error to diagnose exactly which addon is causing the issue.
Change RealUI performance setting - RealUI has 3 built-in settings for speed/performance. If you're noticing issue that involve frame rate drops/spikes, it may help to turn down the performance of RealUI. Click the RealUI icon lower left corner of your screen, and up near the top of the list that pops up, there should be an option to change the performance/speed setting. Try setting it to Economy and see if that helps improve the issue. Of course, if the issue is a glitch somewhere, then this setting shouldn't make too much difference.
Here is a screenshot of Power Mode in Turbo mode:
/memory - Right when the issue happens, type "/memory" and scroll up to see the highest RAM usage of your addons to see if one or two specific addons are causing the issue.
Disable addons - If all else fails, disable all addons except for RealUI and see if you can replicate the issue.
If the issue persists with only RealUI enabled, you can try a fresh reinstall of RealUI. Backup your Interface and WTF folders, then delete them and install only RealUI into your Interfaces folder.
If the issue stops happening when only RealUI is enabled, then the issue lies with another addon. Start enabling one addon at a time to find out which one causes the issue.
If these steps don't help resolve the issue, feel free to create a new thread here in the forums to see if someone can help or has experience with a similar issue. When creating a new thread for a question/issue, attaching a screenshot can be very helpful and will likely yield you better results when asking for help. To take a screenshot in-game, press Print Screen. It helps even more if you can circle the area that shows the issue.