iOS 18 Calendar app hangs regularly with Exchange Server

The hang/CPU utilization was so bad for me I’ve been unable to remove the Exchange account. Charging also stopped due to overheating. Calendar even hung when simply tapping OK to acknowledge notification of an expected appointment.

Same issue with battery usage and phone over heating.

Same problem here with iOS 18 and 18.01. It continued eating my battery to the point where my iPad died from lack of charge overnight.

I also had to disable all of my exchange Mail and calendar accounts, and fall back to Outlook (which has less functionality). I had to turn on airplane mode, reboot, then delete the accounts to get it to stick. (as BennSc noted). I also reported the bug to Apple. I hope they fix it soon!

I had this issue too…first with iPhone 15 Pro after iOS 18 upgrade, then again on iPhone 16 Pro. Narrowed it to the exchange server connection I use for work. Work requires a Hub app that installs a profile used to confirm 2 party authentication. Calendar would freeze, regardless of exchange calendar or iPhone calendars. That would put the phone processor into overdrive, heating it up while draining the battery. iPhone restarts stopped the drain, but who likes rebooting that often. This affected my iPad Pro M4, too. So two iPhone versions & an iPad. I have another iPad w/o the exchange connection that has operated w/o issue.

My solution - completely removed the Exchange connections. A few reboots in between, then reinstalled the exchange connection. That solved my problems. My calendar app is working as it should with all the new functionality if iOS 18. I’ve read on other posts whom have done similar actions, but had the issue reoccur later. But so far, I’m okay (knocking on wood as I write this). It’s weird. Most of my work colleagues use iPhone and the same exchange connections. I’ve not heard anyone else complain about this issue. However, I’m normally one of the early adapters of new hardware and software releases, which maybe explains why not many others have complained about this issue. Keeping my ears open…hope this helps you.

Just an update: I had deleted all of my calendar and email accounts on my iPhone and iPad, and things seemed fine. However, yesterday both devices had their batteries draining rapidly, and it was due to the calendar app… Even though there are no calendars connected to it. The best fix I could come up with was to delete both the email and calendar apps from my phone.

What a pain.

Just installed iOS 18.0.1 but the issue remains.