When a certain number of EXP orbs are on the ground, instead of the player absorbing them all at once, they slowly get absorbed as they orbit the player. This feature has been in the game for a while, but something I've noticed is that if the player looks at the EXP orbs before they get absorbed, they can see through chests. I haven't tested this with other blocks but it seems to not affect full blocks, such as cobblestone.

To recreate this problem, try killing multiple mobs at the same time while standing above a chest, with a hollowed out area beneath the chest for better results. In my case, the only things directly below the chest was three hoppers, which can be viewed in the attached screenshots.

This was done at an Enderman farm in The End, so because of the quantity of EXP, I was able to look through the blocks for quite some time before all of the orbs were eventually absorbed.

The third photo was uploaded as a comparison, to show that the chests are not normally transparent.