This is the same issue as MC-50349.

The bug

Iron bars on top of other iron bars, as well as glass panes on top of other glass panes, will not cull the upper face of the block below them, nor will the lower face of the one on top be culled by the block above them. This causes undesirable horizontal stripes when making large panels out of these blocks.

How to reproduce

1. Create a thin sheet out of iron bars or glass panes
2. Observe from many angles

Expected results

These top and bottom faces would be culled accordingly.

Actual results

They are not.