I’m also running HA with a Nortek stick. I have 23 red series dimmers and 1 red on/off and I personally haven’t seen this. I just checked history on a dozen switches but none appear to have lost connection. Someone posted a similar issue with the bulbs a few days ago, not sure if it’s related
How far away from the stick is your switch? Do you have a small number of zwave devices? I know the switch has a signal strength detector built in, I’ve never used it but I’m wondering if the signal might be weak? Hopefully we can find a solution!