When the player tries to break blocks that are under his feet while crouching, he is pushed to the edge of the block that is closest to him.
This problem apparently doesn't happen with every block, or at least not every time. I've seen this bug with some blocks that are made to be broken by shovels and with the redstone ore block.
I've noticed its existence since older versions, like 1.7.2 and 1.8.10, but it still happens in 1.17.1 and snapshots.
Enchantments that alter block drops such as Silk Touch and Fortune do not influence this issue.
This issue only happens in multiplayer modes, including Realms, Servers hosted on specific machines (like Hypixel and public survival servers) and servers hosted by services like Hamachi and Radmin VPN.
Ping does not interfere, since this problem happens with both 10ms and 200ms+.

Here's a youtube video demonstrating the problem: https://youtu.be/niP4SJONmhQ