M113 is prone to engaging in futuristic tank physics when entering or exiting the water. See videos:
https://youtu.be/D4Y711AxR2w
https://youtu.be/7NJTnOr8BnM
Wheeled vehicles don't appear to be affected. It's also possible that it's related to ponds, as the M113 seemed fine in sea water (e.g. on Malden 2035).