I had a LOT of trouble as well adding my Sylvania Osram Lightify (73741) RT5/RT6 to Smartthings.
Here’s what happened. I installed 6 of these lights inside my living room.
I booted up the Smartthings app, started looking for devices and THEN turned on my lights. Smartthings found the lights and I renamed them all. After it configured the lights I went back to my devices list and it said “Tiles Missing” and would not allow me to delete them.
I did a lot of research and went to Smartthings IDE on my personal computer (desktop). Make an account if you don’t already have one. Once you get logged in go to the “My Devices” tab at the top.
Find the lights labeled “Thing” and click on one of them. Go to Edit. From there change the "Type."
I changed mine to “ZLL RGBW Bulb” and they worked perfectly. I had to change all six bulbs individually to the “ZLL RGBW Bulb” and they were added correctly and worked correctly.
I went back and refreshed my Smartthings app and they showed up correctly there. I was then able to make adjustments such as scenes, brightness, color and it appeared correctly in my Amazon Alexa app.
Hope this helps someone. I did a lot of research and no one had it written out concisely on what needed to be done. Cheers.