Steam deleted half of Apex without any reason

I was launching apex legends when suddenly steam restarted and I found that it wants me to download half of the game again without any reason. 

I had a working backup and I used it many times before and it's working just fine (I tried before to put it on steam and it worked) but when I try to put it on the game folder and validate, it keeps removing the working files and asking to re download half of the game again. What can I do the prevent the game from being deleted as I cant re download it because of metered connection