Want to share that I have discovered that installing a blue series switch in 3 or 4 way mode with dumb rocker switches that light up (Illuminate) when off, causes undesirable results. I am a Home Assistant user and discovered that during my initial installation after pairing to ZHA, the switch had weird behavior. The blue switch as shown in HA and the lit rocker would flash on and off when turned off by the rocker switch. The lights functioned as expected. Going from on-off to dimmer and adjusting brightness did not change this behavior. So Home assistant could not get a clear response from the switch as to what state it was in. Was about to rethink wiring as I had remodeled the area the switch was located in a couple of years ago. I looked hard at the lit dumb switch and decided to replace it with a non-lit 3 way switch, and just like that, all was well.
I looked hard on this site and other sources and did not see this issue. It is possible that my keywords in my searches were insufficient.
Search “illuminated”. But unfortunately, unless you knew that the illuminated switch was the issue, you probably wouldn’t have come up with that as a search term.