For me, it was forgetting the password on the external hard drive. After that, iCloud got to a point where I felt like backing up became unnecessary so I stopped TM.
(I know this isn't the response you were looking for. I've also experienced corrupt TM unrelated to HD encryption, not sure why)
(I know this isn't the response you were looking for. I've also experienced corrupt TM unrelated to HD encryption, not sure why)