Stacked M4300 Switches for ETC Lighting Network - Slow Web Interface

Hello!

We are unable to complete configuration of our (4) Netgear M4300-52G-PoE+ switches as the web interface has become extremely slow. When we try to log in or change any settings, we experience a >1 minute delay between any links clicked on the web interface and any response from the switch.  Often, the response will timeout and we will need to start over.  As you can imagine, this is quite frustrating.

More info: Our switches are configured in a stack with two VLANS: one for management, and one for an architectural lighting control network using an Electronic Theater Control (ETC) paradigm architectural lighting system.  The stack is connected to our existing CISCO network in our building, which allows us to connect to our lighting network using a WiFi SSID set up for this VLAN.  

CPU Usage is around ~30% and memory usage appears to be 90%.  

How can we go about diagnosing and solving this issue?  It is difficult to understand what the issue might be as we cannot complete any normal troubleshooting steps (i.e. downloading logs, etc.)

Thanks!

M4300-52G-PoE+ (GSM4352PA)