If I recall correctly, when installing the viewer with acrobat reader already installed there is an option to make the Xchange Viewer the default for viewing PDF files.
If you decline this offer then at least in theory the thumbnails will be handled by xchange whilst reading is handled by Acrobat Reader.
This is not proven but as long as the Xchange reader is loaded second, it should work
The other thing to watch is of course an auto upgrade of Acrobat may need the Xchange viewer to be repaired
Also with your particular mix of x86 & x64 does this happen on shared data files, what can happen is the x86 reader will create thumbnails which remain until the x64 attempts to create them and fails