He will return back to his bad form after a few matches, you will see. Currently, I'm playing with my lower quality GK too as the other that seemed to be the superior one visually in terms of quality is '****' in terms of performances on the pitch. He is probably one the reasons why my team was knocked-out at the 1/8 round of CL this season. Ratings of 8 for GK may be illusions. Many GKs that appear to be doing nothing significant are earning ratings of 8 (7.4-7.6) This has already been discussed.
P.S: I have had 6-7 star GKs in the past, including one from the scouts' list. There displayed qualities appear to be illusions. There performances on the pitch have been very inferior to what it is expected for such players.