I read a few entries saying that the smoothieboard is disconnecting the first time the laser is fired. This got worse after I replaced the laser tube with a new one. As there is no easy way to replace the board right now we were trying different things to avoid this. Suprisingly starting the laser with zero power helped a lot. We are working with lightburn and this is our solution now.
In the preferences for the machine enter the following gcode before the start:
G00 G17 G40 G21 G54 G91 M3 M106 ; Start something G1X5S0F6000 G1Y-5 G1X-5 G1Y5
This will just draw a square with 5mm at zero power and will return to the point were it originaly was started.
This helped for me.