It has to be raining/snowing to reproduce this issue.
Steps to reproduce in testing/creative world:
Turn on the rain "/weather rain"
Build a wall 2x2x1
Throw any item in front of the wall
Pick the item
When picking the item, you can see the rain through the wall.
I figured it out when I was playing at realm.
Thank you for your report!
However, we are already tracking this issue, and this report is a Duplicate of MC-163575, which is a report that has not been resolved yet.
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