Should be fixed in the next release, but you may not want to jump to the Canary channel for just this.
A workaround someone proposed was to copy the DLLs from another system, like a Windows computer. (Make sure it’s the same version of course.)
I just tested this idea and it worked for me. I copied:
AlphaFS.dll
AlphaVSS.Common.dll
from C:\Program Files\Duplicati 2 and put them in /usr/lib/duplicati on my Linux machine. I do not know if that first one is needed or not, but it can’t hurt.