title: Autolayout center x alignment resulting in infinite layout loop on iPhone 6 Plus
body: <p>Our app is hanging on the iPhone 6 Plus only.  The app becomes stuck in an infinite layout loop.  We have found we can stop the layout loop by removing autolayout constraints that use "center x alignment" and "center y alignment".</p>
  
  <p>Can anyone provide insight into why this is happening?</p>
  
  <pre><code>Thread 1, Queue : com.apple.main-thread
  #0  0x3658bf4e in objc_msgSend ()
  #1  0x29af3962 in __44-[NSISEngine fixupIntegralizationViolations]_block_invoke_2 ()
  #2  0x29aebd88 in -[NSISLinearExpression enumerateVariablesAndCoefficients:] ()
  #3  0x29aedbc8 in __44-[NSISEngine fixupIntegralizationViolations]_block_invoke ()
  #4  0x29ae8de8 in -[NSISEngine withBehaviors:performModifications:] ()
  #5  0x29aed8fc in -[NSISEngine fixupIntegralizationViolations] ()
  #6  0x29aed310 in -[NSISEngine optimize] ()
  #7  0x29af32e2 in -[NSISEngine constraintDidChangeSuchThatMarker:shouldBeReplacedByMarkerPlusDelta:] ()
  #8  0x29af315c in -[NSISEngine tryToChangeConstraintSuchThatMarker:isReplacedByMarkerPlusDelta:undoHandler:] ()
  #9  0x29ae83fa in -[NSLayoutConstraint _tryToChangeContainerGeometryWithUndoHandler:] ()
  #10 0x29ae7f98 in -[NSLayoutConstraint _setSymbolicConstant:constant:] ()
  #11 0x2c3ef516 in -[UIView(UIConstraintBasedLayout) _autoresizingConstraints_frameDidChange] ()
  #12 0x2c2f8b3c in -[UIView(Geometry) setFrame:] ()
  #13 0x2c31833c in -[UIScrollView setFrame:] ()
  #14 0x2c8f03da in -[_UIQueuingScrollView setFrame:] ()
  #15 0x2c8f0168 in -[_UIQueuingScrollView _setFrameAndApplyPageSpacing:] ()
  #16 0x2c8755b4 in -[_UIPageViewControllerContentView layoutSubviews] ()
  #17 0x2c2fbb36 in -[UIView(CALayerDelegate) layoutSublayersOfLayer:] ()
  #18 0x2bd23ccc in -[CALayer layoutSublayers] ()
  #19 0x2bd1f6b4 in CA::Layer::layout_if_needed(CA::Transaction*) ()
  #20 0x2bd1f53c in CA::Layer::layout_and_display_if_needed(CA::Transaction*) ()
  #21 0x2bd1ef20 in CA::Context::commit_transaction(CA::Transaction*) ()
  #22 0x2bd1ed24 in CA::Transaction::commit() ()
  #23 0x2c2f3fc4 in _afterCACommitHandler ()
  #24 0x28e275cc in __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ ()
  #25 0x28e24c8a in __CFRunLoopDoObservers ()
  #26 0x28e25092 in __CFRunLoopRun ()
  #27 0x28d73620 in CFRunLoopRunSpecific ()
  #28 0x28d73432 in CFRunLoopRunInMode ()
  #29 0x300db0a8 in GSEventRunModal ()
  #30 0x2c35d808 in UIApplicationMain ()
  </code></pre>