When there is a dirt block on top of a chiseled stone or plank it can have the opportunity to fall through the chiseled block. When we updated to .16-.17 there were a few scenarios where these dirt blocks were corrupted and caused a feedback tick loop where the dirt block constantly fell into the chiseled block again and again without breaking the chiseled block. This puts a lot of stress on the server and causes it to "timeout" instead of crash where it basically freezes trying to process the event.
I have no evidence to believe this is reproducible post .17 by any player's means. It only seems to be select blocks scattered throughout the world and once they're removed the area is stable again without repeat. That being said, please try to avoid putting your dirt on top of chiseled blocks. This is more likely to happen when people visit places that haven't been loaded by players post .17 update, such as visiting an inactive player's town.