Confirmed happening to us in 19w03c.
Console is being spammed with the "Keeping entity" line and "Can't keep up" lines.
Keeping entity minecraft:item that already exists with UUID 81f33f25-04c4-4fe3-b265-b7e7bfcbd345
Can't keep up! Is the server overloaded? Running 2677ms or 53 ticks behind
Seems to run fine during the day when there are no mobs..
Well, boats we're broken for 5 years. I wouldn't hold your breath. Hypixel will come out and Minecraft will be dead. It's not like they got bought for billions of dollars or have the entire Microsoft team behind them to hire better/more devs.
Yes, I'm salty about another game breaking bug.