Not sure if anyone ever solved this but I just did after having the same problem.
First: make sure you have the “ADD_SMT_109_Triebwerk.vstsound”. (I have a complete backup of ALL my Steinberg VST’s and Programs on 2 separate drives so I don’t have to re-download the 80-100GB worth of files again in case of something like this.)
Second: right click “ADD_SMT_109_Triebwerk.vstsound” and select copy (or any other way you prefer to make a copy of the file)
Third: navigate to C:\Users(YOUR USERNAME)\AppData\Roaming\Steinberg\Content\HALion\VST Sound and check to see if “ADD_SMT_109_Triebwerk.vstsound” is in there - if it is not, paste “ADD_SMT_109_Triebwerk.vstsound” it into this location
Fourth: fire up whatever DAW you’re using, load up Triebwerk and open the “browser”. You should now have ALL the presets again.
This worked for me. I even deleted the presets right out of Trieb and did the same thing I described above again and it still worked.