I’m using WL on two machines which works perfectly … except 
Opening a project on machine two, all plugins are scanned again and the preferences e.g. the last projects list is empty. Now I see I can excludes some directorys for anything (I don’t know).
Exists a way to work on two machines without these behaviours?
The 1st time you load on your 2nd machine this is normal that there is a plugin scanning, but if you load again, does it happen again?
When opening WL on the first machine the plugins are scannend again. Reopening WL on the first machine the plugins are not scannend again.
Maybe its important, the settings are on my DropBox folder. So Both machines are sharing the same settings.
That’s the problem. I would rather advise you to have separate settings, as is the case by default. And when it is necessary, you synchronize with the subfolder of the presets.
I have used 1 or 2 additional machines over the years (currently using 3 machine total) and I always manage the preferences setting manually for each machine instead of attempting a Dropbox sync.
I find it pretty easy to update the Preferences folders(s) manually as needed if I change something big (or not so big) on my main computer that I’d like to be present on the other two.
Because some Preferences & Settings paths are relative to each machine’s file path specifically, trying to use a Global Preferences folder on Dropbox seems like a bad idea.
That said, there does seem to be some kind of native option in the WaveLab Preferences area that I have never tried:
