Strange Intermittent Network Connectivity

[cbaleos01]

I hope someone will take time to help us. We are not actually using Cisco switches. Ours are from HP but I just want  to try my luck here. We've been experiencing connection problem for almost 2 months now. When the issue happens, random PC  loose connection to the to the server but it doesn't last long. Most of the time the issue happens for several seconds to 2 minutes at the most. 

Here are the different scenarios that we encounter:

Scenario 1:

Workstation 1  -----> server 1 == continuous ping

Workstation 1 ------>server 2 === continuous ping

Workstation 2  ------>server 1 === continuous ping

Workstation 2  ------>server 2 === request timed out

Scenario 2: 

Workstation 1  -----> server 1 == request timed out

Workstation 1 ------>server 2 === continuous ping

Workstation 2  ------>server 1 === continuous ping

Workstation 2  ------>server 2 === request timed out

Scenario 3:

Server 1 ------------> Workstation 1 == no packet loss

Server 1 ------------> Workstation 2 == no packet loss

Server 2 ------------> Workstation 1 == no packet loss

Server 2 ------------> Workstation 2 == no packet loss

Note: I also attached the detailed topology of our network and the troubleshooting steps that weve done. Thank you so much in advance. 

[Philip D'Ath]

What was changed on the last week of March?

I see you have a firewall in between everything, a Cyberoam.  Anything in its logs about blocking?

[cbaleos01]

We did not change anything since  the last week of March. The last changed weve done was that we updated the firmware of the firewall last January.  What kind of blocking in the logs of the firewall should we check? My colleague already checked the configuration as well as the logs of the firewall with the manufacturer and they did not find any suspicious events.

[Leo Laohoo]

Most of the time the issue happens for several seconds to 2 minutes at the most. 

Sure it's 2 minutes and not 55 seconds?

[cbaleos01]

maximum is 2 minutes. average most probably is 55 seconds

[Leo Laohoo]

maximum is 2 minutes. average most probably is 55 seconds

55 seconds is the time it takes a computer to join a network when spanning-tree portfast ain't enabled on the port.