Note that the Segment Editor in Wwise displays PCM data at 48 KHz. Whenever the converted file is resampled, or compressed, the actual sample values will be different than what is displayed. One of the consequences is that you should not trust any editing you make in Wwise to fit the zero-crossings.
Codecs that have inherent latency or a volume ramp up (due to FFT windowing, like Vorbis) will always start being heard slightly later than what is shown in the Segment Editor in Wwise. This can create short gaps between segments. You should always test your transitions (from one segment to another) when using compressed audio data. If needed, add some post-exit and/or a small fade out to cover up for sample inaccuracies.