Can't keep up! Did the system time change, or is the server overloaded? Running 5349ms behind, skipping 106 tick(s)

Hi, me and my friends have played on this server for 2 days now, but last night and now again this morning, we have gotten sick lag spikes that last forever. Could someone tell me what we have done wrong? I have read the article about lag, but it doesn't tell me what we did that caused too much load on the server. Roman

https://mclo.gs/LQvfMEn