In 1.13 and prior, the end portal frame reused part of the end stone texture for the bottom half, which caused it to seamlessly blend in. However, after the Texture Update, a significant break can be seen between the two blocks. I suspect that this is due to the End Stone texture being updated twice in 1.14's development, whereas the frame was only changed once.

A specific setup may need to be built as to mitigate the effects of MC-165504.