Is there a reason why many of my devices have simply become INACTIVE and are not responding to any commands?
I'm including a screen shot, which shows many types of devices (switches of different brands, outlets, a siren, etc.)
For me, it appears to be an issue with that column updating
After just opening the devices pages
Here it is in the z-wave page
It responds fine.
EDIT: Noticed it was a z-wave plus with a standard driver changed it smart driver. turned it on and off, did a refresh. Device pages still shows 11-28 date and inactive
Active vs inactive really is just when the devices sends something back to parse. If the device hasn't done this after awhile it gets marked inactive, because, well, it is.
If a device is unresponsive, that could also be a cause.
I have to repair a lot...normal I think. I have a bunch of sylvania bulbs and switches and they do not stay paired...mainly the far ones since they are terrible repeaters
Help me understand the difference between the time stamps of "last sent" and "Last Received" on the z-wave page and the "Last Activity" time stamp on device page?
Last sent and last received on Z-Wave page reports the actual packet traffic. Last Activity is the date / time of the last device event sent by the driver.
I notice my Z-wave outlets frequently say "Inactive" but they always respond when I use them. It seemed odd to me since they are plugged in and have power all the time. Since it doesn't cause a problem I am learning to ignore it.
For me, I have had a number of devices not only showing up as inactive, they have also become unresponsive. I've tried to reboot my hub, run zwave repairs, etc. Nothing has helped.
So, I've gotten in touch with support to see if they can help straighten out the issue.
Repair a lot? Z wave repair is not needed if you are leaving the devices at the same place, but you mentioned Sylvania, I think those are zigbee, and there is no zigbee repair, just turning off zigbee radio for more than 15 minutes to force them to update.
It's the zwave devices that are going inactive(even zwave plus). Furthermore, I don't understand how an outlet, can become unresponsive to zwave commands from the hub. That's why I contacted support.
Inactive is normal, not every device will send data to the hub unless you send a command to it, but unresponsive is different, it could be a bad device or bad mesh, I'm managing 4 hubs and all are working fine, I had an unresponsive device and it was a bad mesh, the device needed a repeater in between. You contacted support and it's good because they can look further, please post your results so your case will help others.
I have tried to ensure that there is no device without a repeater between it and the hub, with no distance between devices greater than 20-30 feet. Hub is centrally located. Every device that is plugged in (primarily outlets, plugins, and switches) is a repeater.
Furthermore, I have run zwave repair many times to ensure that mesh inconsistencies (due to bringing the hub close to device to pair), are "ironed out".
Worked fine in SmartThings - not sure what the problem is. That's why we have support.
In OpenHab/Home Assistant there are z-wave network topology tools that help straighten out these issues, that are user accessible.
OpenHAB and Zensys Tools
HomeAssistant and OZWCP
"We" have access to both as well... just not as cleanly wrapped. 
