I suspect you will have to turn off the live focus feature if you want to continue using LightBurn with your laser, since it isn’t supported in our software.
This post mentions the LFS-PM-T43, which from my understanding is your live focus feature. It may be as simple as unchecking the z movement in LightBurn, but I can’t say for certain!
Please share screenshots and a LBRN project file of the job setting where you do not get laser output, so that we may investigate further.