As a test and to just get things running well, we reinstalled the 3120 I had been using.
No issues with that. It always ran well for me previously anyhow.
Curious though if the 3140 would give me more bandwidth make better use of the speed. I do want to put it into service if possible if it makes any sense.
I don't have an answer for you, but I do have a 3140 that I port scanned on the LAN side using Angry IP Scanner. I can see the 3140's firewall wasn't too happy about zero byte connections, so a number of messages popped up on my CLI session while the port scan ran. I did not, however, ever lose the ability to ping or administer the 3140.
About my setup
NV3140, running R12.3.2
Angry IP Scanner 3.3.3
Port range 1-1024
Default port connect timeout 20ms
Adapt timeout to ping - checked
Minimal adapted connection timeout 10ms
Perhaps your 3140 is running out of firewall policy sessions or hitting max CPU during your port scanning. Check both by using "show ip policy-sessions peak" and "show proc cpu realtime" commands. If all looks good, I'd compare the configuration between your 3120 & 3140.
Hope this helps,