Error: null is not an object (evaluating 'a.__AMP_TOP') #9177
Description
A typical stack is:
$b@https://cdn.ampproject.org/rtv/001493923946479/v0.js:52:297
at __AMP_TOP(https://raw.githubusercontent.com/ampproject/amphtml/1493923946479/src/service.js:342:9)
at win(https://raw.githubusercontent.com/ampproject/amphtml/1493923946479/src/service.js:177:21)
at window(https://raw.githubusercontent.com/ampproject/amphtml/1493923946479/src/services.js:303:17)
at element(https://raw.githubusercontent.com/ampproject/amphtml/1493923946479/src/custom-element.js:1646:15)
at https://raw.githubusercontent.com/ampproject/amphtml/1493923946479/src/custom-element.js:1249:30
at inViewport(https://raw.githubusercontent.com/ampproject/amphtml/1493923946479/src/service/resource.js:759:34)
at shouldBeInViewport(https://raw.githubusercontent.com/ampproject/amphtml/1493923946479/src/service/resources-impl.js:1360:22)
at discoverWork_(https://raw.githubusercontent.com/ampproject/amphtml/1493923946479/src/service/resources-impl.js:1860:36)
It appears it fails to request vsync service for an element because element.ownerDocument.defaultView is not available. A most likely cause is the race condition b/w browser's iframe cleanup and resources cleanup in AMP.