@Ulf, I have resolved the difficulties with my La Mer file and hope my discoveries prove useful to you and other users who also had files that failed to load and playback and then required Dorico to be force quit. Apart from these problems, the most noticeable factor was the large number of instrument files for string instruments for which independent voice playback had been initiated.
Most of my Dorico files have involved smaller instrumental forces and this file was an early attempt at using Dorico for orchestral scores and in particular, for inputting string instrument divisi in galley view. I delighted in creating the appropriate number of staves to accommodate divisi but foolishly neglected to input all music in each stave into the default voice (upstem 1). As a result, most of my divisi staves originally included music in two voices and when I elected to activate independent voice playback for each of my strings, the number of instrument tracks was in all cases higher and in some cases twice what was required for the music. This undoubtedly impaired Dorico’s ability to assign a single appropriate instrument to each divisi track. (I had also mistakenly added an unneeded cue staff for 1st violins but neglected to delete it.)
My initial attempt at a remedy with the file you rescued for me involved highlighting the music in each divisi staff and changing it all to upstem voice 1 in the hope this would get rid of the excess instrument tracks. However, this didn’t work—the number of instrument tracks remained the same even though many were empty of music.
I then created a duplicate section player for each of my string instruments and adjusted the number of divisi staves at each point and then copied and pasted in the music which was already solely in upstem voice 1 as noted in the above paragraph. This did successfully reduce the number of instrument tracks. I’m not sure why but it also meant that my solo violin and solo cello parts were no longed assigned to section instruments as they had been, something I assume was a related problem. (No changes were made to any playback templates. These were not the cause of this problem.)
Ultimately, this has been a valuable learning experience for me and I will be delighted if it also helps a long-standing issue for you involving files that fail to load and playback and then require Dorico to be force quit. I realize there may be other factors relating the requirement to force quit but the fact that my changes to the divisi staves means that solo instruments are no longer assigned to section instruments (which appears on the surface to be unrelated) gives me hope that the problems you mentioned might also relate to problematic note entry into divisi staves.