Welcome, 卖扣就是顺口!
From your post, it sounds like you are having issues with calendar invites you have created. We're glad that you reached out to the Apple Support Communities. We want to try and help you find the answers you need. To verify, what type of iPhone are you using? Which version of the iOS software do you currently have installed on your device? You can find this in Settings > General > About.
Does the problem happen within all calendar invites you have created? If you have not already tried, Restart your iPhone. Does this help to resolve the issue? Often this simple step will refresh the apps and software on the device to solve numerous problems you may encounter.
Take care!