the reason I asked is i had a bad experience with it but a while ago. that i remembered right after we talked about your issue and i meant to come back here but forgot. and yesterday someone asked again about persistent data here and it reminded me to comeback and suspect it more
the issue i had is i was having a complex rigged character with organic and mechanical parts, the mechanical parts were just parented to the bones (no weight painting) i was never able to render this scene with persistent data what ever i tried
since it was a heavy scene i used persistent data to help with speed and started a render that i waited for almost 24h hours. when i looked at the results i was 
the mechanical parts were randomly getting scaled huge or shifted from their position for one or two frames through the animation.
i assume the lantern light is parented to the person rig.
so it’s a bug that i’m not sure it’s fixed completely (specially that it’s hard to reproduce), it traumatized me and never used persistent data again to be sure, but yesterday someone is complaining about loosing bevel modifier when using persistent data 
so if you don’t want to give up on motion blur and still want to figure out what it is and you can give it a try without persistent data 