You'd benefit massively not shooting directly into the sun, also try tilting the gimbal/camera down a little

Thanks. ill try that next time.

ND filters are mainly (just) for reducing the shutterspeed.
If you want to reduce glare, you might be better off buying a sunhood (and take from different angles)

The video was quite dark, then suddenly lightened around 1:15.  What changed?  

I was playing around with the settings. A lot to learn..