The ratings for goalkeepers are often inexplicable.
I've seen 'keepers make several saves and get a 5 and I've seen them make no saves and get a 9.
My current 'keeper had a game last season where he saved 2 1-on-1 chances, intercepted several corners and crosses and saved a penalty. I conceded 3, so he got a 5. Saved me from conceding an extra 4 or 5 goals...
If I watch the game, I try to judge it based on the commentary.
I wish I could explain it to you. I suspect that, if you're losing, all the ratings are affected.