Server skips 370+ ticks periodically

Aikar's Timings Viewer timings paste

Errors often look like:
22.02 21:38:22 [Server] Server thread/WARN Can’t keep up! Did the system time change, or is the server overloaded? Running 20655ms behind, skipping 413 tick(s)

Server often has at least 10 or 15 people on it, with no real signs of this dying down for a long while.