I've had this twice since updating to 9.5. - Just this weekend in fact. I have fixed with a active full on one job, and will fix the other tomorrow. Is this a bug or something we need to know about?
Just registered to support this claim - actually found this thread by googling: Previous full backup chain transformation failed Error: Not transformed OIB was not found. CreationTime
This was not an issue in 9.0, and cropped up the night after we upgraded to 9.5 Update 1, which is the first time this job ran post-upgrade.
There are over 3 TB free in the repo, and I'm running an Active Full now. If that doesn't work, I'll open a support case.