Falling through the map

Platform:
PC

Steps To Reproduce:
Unknown. was playing through the First Contact mission and suddenly was falling through the map over and over. tried traveling to safehouse and as soon as i walked outside the same thing happened. i had to exit and restart the game for it to stop.

Images / Videos:
on steam account

Host or Client:
Steam friend

Players in your game:
2

Specifications:
intel I7-6700K
8gb DDR4 2400mhz
RX480 8gb
Intel SSD
750W PSU