Export failure in Cubase 8.5

I have a problem with groups muting when exporting in Cubase 8.5 PRO

I have had this problem when exporting the final mix on my laptop, but never on my stationary where I normal use Cubase… I haven’t done anything about it on my laptop, since I rarely export from there, but suddently it does the same thing on my stationary, which it has never done before…
I have all the vocals send to one group and all the music to another group… When I listen to the final exported file, at some random place in the song all the music just stops, and the song is acapella the rest of the song… Nothing changes on the vocals, everything is the same with fx tracks and everything, but the music just mutes… I have been exporting this song maybe 10 times without any problems, but suddently it made this error twice, and the music muted in two different places in the two errored mixdowns… And it’s not on a beat or anything, and nothing perticular happens at those to points in the mix… It’s very annoying…
As said I have seen it before on my laptop, but I have made many many mixdowns on my stationary computer without ever having this problem… But now suddently it does it on the stationary also… Before I just thought that it was some hardware failure on my laptop, which is not really made for music production, but now that it also does it on my stationary computer, which is made especially for music production, I guess it is not a problem with my laptop, but a problem with Cubase…

Has anyone experienced this issue before, and what can I do to fix it?