IOS 15.5 Calendar Events Won’t Delete…

AHA! By “close out of calendars” do you mean you go to the multitasking screen and swipe up to close the app? That is what is causing the problem; you close the app before its next scheduled sync, which is not instantaneous. STOP DOING THAT. NEVER swipe up on any app to close it, because it can cause similar problems with many apps. The ONLY time you should “close out an app” is if it is misbehaving. While it is counterintuitive, closing apps increases energy drain on the battery and slows down your phone. See→Do not close "background" apps | Communities

Birdiefan wrote:

”Thank you for trying to help…I only use Apple Calendar. iOS 15.5 iPhone X.”

There is no such thing as an “Apple Calendar”. There is an Apple Calendar APP, but it just displays the calendar on the server or servers that host your chosen calendar. Go to Settings, tap on Calendars, then Accounts. These are the server or servers that host the calendar or calendars that are displayed in the Calendar app. Look them over, and report which one specifically says Calendar, or if more than one say Calendar tell us what they are.

The master copy of calendars is on a server, usually the server for your email account. If you don’t have an Internet connection when you delete an event the server isn’t updated, and the event will reappear when you do have an Internet connection. This is not an iPhone issue for Apple to fix; the problem, if there is one, is with the provider you are using to sync calendars.

While you are in the app just swipe up from the bottom of the screen to go back to the Home screen. But none of the apps in the multitasking page are “on”. While you are free to use your phone any way you want, you are not using it according to best practices.

On your calendar problem, what is the calendar server you are connected to? iCloud? Outlook? Yahoo? AOL? Google? The calendar app is just a way to view calendars that are hosted on other platforms.

You should never close apps, unless they are not working properly. Apps in the multitasking list are not running, they are suspended, and most of them aren’t even in RAM; only the 4 or 5 most recent ones are. The list is just a pointer to reload or restart the app quickly. The last time I checked (I don’t often) I had 120 apps listed on the multitasking screen. But read the link I provided for more details.

Greetings Birdiefan,

Welcome to the Apple Support Communities. We see that you have not received a reply to your question yet.

Which account are you using to sync Calendar data? Which specific software version are you using?

Are you able to replicate this issue? If so, which specific steps to you take to do so?

Are you receiving an error? If so, what is the exact wording of that error?

The more detail you can provide, the better the chances of receiving a reply.

Cheers.