Okay, either syncing issues or low tickrate, although we can only guess without seeing it.
The latter can be caused by a maxed-out CPU, meaning that your world cannot complete all the calculations per tick necessary to keep your world running at realtime speed. Things can get very messy from there.
High CPU load can be caused by other programs (such as antivirus activity, program updates etc.) running in the background. There's also a known glitch with liquid updates; when there is a lot of liquid that needs to calculate a new path to flow down, it can really bog down the client. This can get nasty with quarries where people intentionally place water inside the quarry, which then glitches out when a fast-moving quarry keeps digging out the blocks it tries to flow on. This is a vanilla bug, mind you, it's just that the quarry provokes it. Nukes and other large explosions near liquid do as well.