As far as I understood from your description, I think I found the problem.In the second image that you attached, I noticed that you setting the material into "M
at Interface" variable in Game instance ref
But in second image that you attached I noticed that while loading the data you are referring a completely different variable “Mat Skin M”
may be if you refer to same variable that you set the new material into ,you can get the result that you are expecting.
And also avoid using “Get All actors of class” as it is a very heavy node, instead of that you could try using “get player character” and cast to you BP Survival character (Your character). As there will be only one player you don’t have run any additional for each loops.
I Hope my answer is helpful. Cheers!