I have found, more often than I like, that Windows will not release the COM port when you disconnect or turn off the laser. It is a Windows thing.
Sometimes plugging in the powered up laser and unplugging it (USB) will clear it. Sometimes I had to power down the laser and restart Lightburn.
For a while, I had a really bad time with my SF-A9 laser. The solution there was to shut everything down, boot the PC, launch Lightburn, turn on the laser, and then plug in the USB cable. I never did figure out what I was doing to make this happen, but I must have finally quit doing it.
Bottom line is Windows did not release the COM port and you have to correct for that.
This says your Device setup is likely correct, or was…