This is NOT a duplicate of https://bugs.mojang.com/browse/MC-63590, so do NOT close it as such. This problem is new to 1.14, and is making the game virtually unplayable on multiplayer servers.

CPU and RAM utilization are low, but the server is constantly spewing "Can't keep up"/"missing ticks" messages, and players are experiencing horrendous lag trying to break blocks and just move around the world. This is on a vanilla 1.14 server installation. This bug needs to get fixed and sooner rather than later, because in conjunction with the chunk rendering issues that were introduced in 1.14, the game is basically unplayable in its current state.