Unknown error on video on Galaxy s6 but just ONE video- not all

[AC Question]

Last week I filmed a few videos with my Samsung S6. @-3 days ago I showed the video in question (just one of them) to somebody, so that moment the video was fine. I started to upload the video on google drive. Next thing I know: the video on the phone can't be read anymore "unknown error" and the file instead of 1.5Gb became 2kb and the uploaded file on google drive is 2kb- and google drive says he doesn't know how to open it. And justs to clarify. The other videos are safe for now. Thanks,