If you have a lag issue, it’s best to make a .nps file that you can send to the developers so they can investigate further.
Installing Sampler
Sampler is a mod by Player that generates .nps files.
You can download it from https://forum.industrial-craft.net/thread/10820.
For Minecraft 1.12
http://files.player.to/sampler-1.73.jar
For Minecraft 1.11
http://files.player.to/sampler-1.72.1.jar
For Minecraft 1.10
http://files.player.to/sampler-1.69.3.jar
Running Sampler
Then you can /sampler start
and /sampler stop
while it’s lagging.
Then a simple /sampler export [name of exported nps file here]
will write out the .nps file that can be read by the developers in VisualVM.
Important: where to run Sampler?
Is it a lag issue on the server, like tick lag? Run Sampler on the server, NOT on your client!
Is it a lag issue on the client, like FPS lag? Run Sampler on the client, NOT on your server!