Hi,
well, first off you have to know that the Epilog-driver behaves like absolute garbage. Besides its quirks it crashes a lot because it is not really optimised to run under system environments newer than Windows XP. Nontheless we have it running under Windows 10 which works quite well, but you have to bear certain things in mind.
First off, every document must have the exact size of the laser bed. If its smaller than this, it is probable that rendering problems will happen.
Second, everything you want the laser to cut out must be in vector form with a stroke width of 0.01 pt (just type it in, it will show as 0 pt after you pressed "Enter" but it will work).
Furthermore, you must set all the laser settings in the Print--->Settings Menu in Affinity Designer. Changing options later in the Epilog Manager after you pressed "print" will cause a mess with a high probability.
This should hopefully help you quite a bit
Tom