This is the third time this has happened.
I have broken and replaced my shulker boxes dozens of times, maybe over a hundred times since 1.14.4 was released, this has only happened 3 times

each shulker box had been recoloured, and two were named i think.

I mined my brown shulker box unnamed in the overworld, at height 5 with my diamond efficiency 5 pickaxe. shulker box breaks, but no shulker box item appears to pick up. there were at least 5 blocks of air above the shulker box, and clear space in 7 of the 8 surrounding blocks i believe

I placed my white shulker box named "valuables" in a dispenser inside spawn protection. I pressed the button and shulker box was placed as usual, i accessed the box and pressed the piston button to return the shulker box and it broke, but I could not see any shulker box item, i logged out and in, and saw the item for a moment, but it vanished almost immediately and i was unable to pick it up, no amount of moving through the space or re-logging restored the box.

I mined my orange shulker box named "highway wood" in the nether, at height 100 with my diamond efficiency 5 pickaxe. shulker box breaks, but no shulker box item appears to pick up. there were at least 3 blocks of air above the shulker box, and 3 of the 8 surrounding blocks were air, 2 were oak plank slabs and 3 were netherrack . I was pushing against the box when it broke.

Attempting the same manoeuvre of pushing against a second shulker box while mining it mined it normally