This is on a Dell XPS 8700 SE, Windows 8.1.1 x64 Professional with 24 gbytes RAM, 30 mps cable connection, SSD drives, and WWL V7.2.15
Infrequently WWL will hang indefinitely in RAM at 12.5% CPU activity with no error messages or any indications that the program is hung. It has to be killed and restarted to release the problem.
I have a Process Explorer dump of the program while it is hung if you want it. It is 77 mbytes in size (zipped), so please provide an upload instruction if you want the dump.