linux slow dow / where would i look to find the issue

I have also seen this.

I am watching it run with the system monitor. When Quartus starts for a brief time it uses all available cpu cores at 100%. Then I see a small amount of network activity, and zero (0) cpu usage for 200 some odd seconds, a short burst of cpu activity, a blip on the network port, then several hundred more seconds of what looks like it just sitting and waiting.

There are times when it does not do this, and the build happens very rapidly.

It's possible that it's doing a web-access, waiting for a timeout, then continuing. I have the talk-back feature turned off - my guess would be that turning it off only disables the send, and not the wait for reply.

Another possibility is that it (Quartus) is un-happy about the Java version installed. I often see random Java errors when running the tools.

When my schedule is a little less hectic I will investigate more.