This has existed for a long time, but this problem happens particularly often with villagers it seems. I'll go to place a block, and then as I'm doing so a villager walks in the way, and the block becomes neither placed nor in my inventory. If I rejoin the world or server it reappears in my hand.

It's not a big deal, but it's rather frustrating and I'm surprised this issue has been around as long as it has, as I'm sure it was around at least as long ago as 1.14.

This definitely happens on servers and Lan, but I am less certain about singleplayer.