Lags when mining sand?

Hello,

today we had event on our server - treasure finding.
The goal was to mine sand and find chests with treasures.

But when players started with mining, server got epic lags and TPS dropped from 20.0 to 13.2

Here is timing
SHORT SAMPLE -> http://aikar.co/timings.php?url=2561032e49cd19bfb87934829b8f6fcd
LONG SAMPLE -> http://aikar.co/timings.php?url=f7b73485ed0f6d9150889e43fcc17bc7

Any ideas?
Thank you