I have been very happy for this function - but I have a problem using it now it just crash
when I try to align to reference.

The size of the audio is maybe to 2*1 hours recordings I need to synchronize.

It's strange it stopped working - but because it stopped working in my 9.2 installation
I did a update to 9.3 just to see if it would be working but my result was the same.

I really don't know what is the reason for the kdenlive to crash.

I can set the audio referance, but as soon I try to align a track it starts working
and the it just exists out...

Any suggestions ?

I had the same problem as you.
I solved it by cutting a smaller part (a few minutes) of the long files and aligned the smaller files with each other. Afterwards I just aligned the longer parts after the smaller files.

I have tried cutting clips to smaller parts - but this does not solve my problem... it just crash both using 9.2 and 9.3 develop version
so am now forced to do it the manual way.

I have tried making both the the align to file and the set audio track smaller about 2 minutes - i did not work.

How smaller did you use?

It does not give my any bug message - and it have been working fine before with bigger files for me.

The original videolength (including audio) was 20 minutes and the separated audio length (recorded with Zoom H4n) was 90 minutes.
I just cutted only about 17 seconds off both files and this was no problem to sync.

I guess you only synchronized 17 seconds - I have synkronized bigger parts... one with zoom h4n audio for about 1 hour
and maybe half an hour recordings clips in SD format, and some parts in HD - so it must be broken now but I don't know
the reason for the problem. Now I have made one hour of video file in mkv with Manuel synchronized audio tracks from
the zoom h4n and need to place recordings on the track above.