I need to sync 2 audio tracks.

Hi,

I recorded a ~90 minute live music show with two audio recorders. A Zoom H4n and Zoom H5. The H4n was recording ambient with a stereo mic and the H5 was plugged into the soundboard and recorded the vocals track. I need to sync these along with the video that I shot. I normally use Plural Eyes to perform this, but there is an issue with the audio tracks. I can manually sync the audio tracks based on the wave form and my ears at the beginning, but after about 3 minutes, one of them begins to drift and it gets farther and farther away. Both are recorded at the same sampling rate - 44.1Khz. One track is ~1GB and the other is ~500MB both in .wav format. Would love some help on this.

Thanks!
-Bryan