You might have accidently checked "Re-use indirect lighting" in Render settings?

How obvious this is depends on the difference between the indirect lighting in the original and the current render. In general it is not recommended unless it is the same scene with little differences that effect indirect ligthing. It can be used to speed things up if you just tweak the scene or add minor elements. It can also save lots of time in animation if conditions don't change drastically from frame to frame.

Otherwise the pre-pass is still there if you use GI or GR lighting.

Ciao

TD