Improve stability of switches to respond to pings

we have been experiencing a very weird issue where our switches stop (or a slow 1000+ms response) responding to pings, but seem otherwise responsive on the web interface or to snmp polling, and continue to send syslog messages. this happens to all of the switches in this layer2 campus at the same times , all are netgear switches, mostly GS752TPv2, with some v1 & v3's mixed in. they all stop responding at the same time, around closing each day, and start working again the next morning, but it is not always that consistent. a few of the switches mgmt interface is even on another older vlan, and they have trouble also. we are not noticing any other switching issues during these times, we have restarted them, and when the issue is occurring it comes right back after a few seconds. cpu load is not higher then the rest of the day, if anything it and the packet flows are lower then normal. i have a few other smaller locations with almost the same setup with no issues. we re organized the primary wringing closet to install a new vendors gear around the time it started. just looking for any ideas on what could be causing this. is there some broadcast traffic flowing through the switches that are causing them to be slow to respond to pings? i setup a monitor port and sniffed some traffic when it was occurring but nothing jumped out at me, did not see much traffic to the mgmt address. just looking for any ideas of where to dig, we are not seeing any traffic disruptions on the network , just these switches becoming slow to respond to ping.