For starters, I am not electrically capable, so bear with me. But, I did read similar questions that did not address, as far as I could tell, what I see happening (they may have, but I was too illiterate to understand).
I hired an electrician to replace an existing chandelier (19 years old, including dimmer switch is 19 years old). I bought 6 expensive ($10 each) Energetic LED soft white 3000K bulbs. These are marked 'Dimmable'. The chandelier is on a dimmer switch where off has meant off, in the past.
I installed 6 bulbs into the chandelier, turned them on bright. All is well. Turned them off, they remained 'on' (rather dim, but still not all that dim).
I also bought $9 bulbs (not dimmable) for another fixture. I also have a lamp nearby with the old fashioned light bulb. I unscrewed 1 of the 6 on the chandelier. It, of course, went out. The other 5 stayed lit. I then screwed in the old fashioned light bulb. All 5 LED lights went out!!! I turned on the light switch, and all 6 turned on. I turned it off and then unscrewed the old fashioned bulb - all 5 LED came back on!!!! I then replaced it with a $9 LED bulb, non dimmable. $9 bulb did not light. But the 5 LEDs that were still glowing continued to glow.
So, I have a problem. I want the lights to go off when turned off. Might the problem be the bulbs? The wiring of the new chandelier? The age/wiring of the dimmer switch? Something else?
Hopefully, you can tell from the content of this, that I know very very little. If you start talking to me about MOSFET, capacitors, snubbers and the like, it will likely go over my head. I will ask my electrician to come back out, but thought I would see what enlightenment I could obtain here.