Just an update, On iOS 18.4 everything is working normally again.

Hi, Do you have any update on this? If I file a feedback report in Apple Feedback Assistant, how do I link it to this post or to your report?

Hi, I had not tested on iOS 18.2 yet. test_TestStr1() works on iOS 18.2, but on a slightly more complex case it does not. Bellow is another test with a new function test_TestStr3() that works on iOS 17 but not on iOS 18.2. The results of the tests I made are for the 3 functions bellow are: iOS 17 - All 3 functions succeed iOS 18.1.1 - All 3 functions fail iOS 18.2 - test_TestStr1() passes the tests but the other 2 fail. import XCTest final class TestStrings18Tests: XCTestCase { override func setUpWithError() throws { // Put setup code here. This method is called before the invocation of each test method in the class. } override func tearDownWithError() throws { // Put teardown code here. This method is called after the invocation of each test method in the class. } func test_TestStr1() { let str1 = "_%\u{7}1\u{7}_"; let str2 = "%\u{7}1\u{7}"; let str3 = "X"; let str4 = str1.replacingOccurrences(of: str2, with: str3); //This should be true XCTAssertTrue(str4 == "_X_"); } func test_TestStr2() { //For testing that bug in iOS18 still exists let s1 = "TVAR(6)\u{11}201\"Ã\"\u{11}201\"A\""; let s2 = s1.components(separatedBy: "\u{11}201"); let t1 = NSString("TVAR(6)\u{11}201\"Ã\"\u{11}201\"A\"") as String; let t2 = t1.components(separatedBy: "\u{11}201"); XCTAssertTrue(s2.count == t2.count); let c = s2.count //This should be True XCTAssertTrue(s2[0] == t2[0]); } func test_TestStr3() { let str1 = "€_%\u{7}1\u{7}_€"; let str2 = "%\u{7}1\u{7}"; let str3 = "X"; let str4 = str1.replacingOccurrences(of: str2, with: str3); //This should be true XCTAssertTrue(str4 == "€_X_€"); } }