Another player suddenly started not being able to place torches or other blocks when the server time rolled over to the next day.

I'd see them move and make the animation for torch placement on my machine (with the server running); they'd see their inventory count decrease; but no torch would be placed in the world.

Them logging out and back into the server didn't help, restarting Minecraft didn't help.  After they updated their local PC's time to be current on the same day as the server PC (both on the same local network and timezone, PST), then they were able to interact with the world again.

Seems like message timestamp validation could be effected by the local PC time and the server rolling over a day?