Half of tracks are exporting out of sync

I had just exported some vocal demos onto different tracks and when I opened them up in a new session, half of them were exactly as I had mixed them down and the other half were around a half of a second delayed.

I had two plugins on each of the tracks, a gate(stock Cubase gate) and a compressor(JST Gain Reduction). Both were bypassed on every track during mixdown. Anybody know what seems to be the issue?

Thanks in advance.