Contacts searching often fails, for contacts that are right there. Also, when using apps that somehow depend on contacts they present a noticiable slow-down.
For example, in Whatsapp often time it takes some seconds for a message to open, and when I make or get call I first have to wait about 15-20 seconds for the call to start or for I to be able to answer.
Similarly, on normal calls when I close the call the phone screen stays open (and I cannot kill it) for 15-20 seconds.
Also on Telegram it takes about 15-20 seconds to see messages once I click on them.
My setup:
I have an iPhone 17 Pro Max with iOS 27 (they same was happening with the latest version of iOS 26 before updating to iOS 27).
I have about 3,500 contacts, and although that sounds a lot the reality is that my old iPhone 15 Pro Max with iOS 25 dealt with them flawlesly.
Note that at one point I decided to reinstall iOS 26 from scratch and reinstalled all my apps again from a backup I made on my Mac, and that didn't fix the issue.
I also try turning off and on Contacts Search on the iPhone, rebooted, to no avail. This has been going on for several weeks now ever since I bought the new iPhone.
This is extremely frustrating.
Potential hint as to what may be going on (I'm a software developer so I can see some patterns here): When I updated to macOS 26 on both my M1 Mac Studio and on my M5 MacBook Air, I noticed that all contacts-related processes were eating a lot of my CPU time, sometimes I had to kill them, I also disabled Google Contacts synchronization to no avail just in case.
During all of this, my iPhone battery drains pretty fast as well btw, much faster than my iPhone 15 Pro Max, and the iPhone usually gets warm.
So this could be related to some sort of contacts-related background process that affects all macos/ios 26-and-up versions of Apple's OSs.
I wonder if something like this is happening to other people, this might be an urgent issue for Apple to fix.