X10 is very susceptible to powerline noise, and there is a lot more today than 20 or 40 years ago mostly being introduced by the increased number of AC-DC power adapters/chargers that are used in most homes as well as solid-state devices using AC-DC transformers for their circuit boards.

Despite that, I continue to reliably use a half-dozen or so X10 devices and a 25-year-old CM11A controller which are now integrated with my Home Assistant setup. Never worked with any alarm/security components.

When powered ON, any unpaired Zigbee bulbs will indicate they are in paring mode by a single episode of blinking or cycling through colors or color temps. They should only remain in pairing mode for a few minutes - and won’t go into pairing mode again until next time they are powered ON.