Yeah, I've been saying for quite a while now that there was a clear starting point and continuation to Goff's troubles. Since that KC game, he hasn't been the same QB. Putting up 54 points in prime time for all the league to see, IMO, woke the dragon. Defenses went to extra effort to diffuse what the Rams were doing.
I have also contended that what made things so easy for Goff(under McVay) have also retarded his growth as a QB. That year and a half of headset communication, clean pockets, wide open receivers and a dominant running game all combined to make Goff look a lot better than he actually was. Kind of like when a QB playing for a college powerhouse looks good. Not a lot of pressure, clear passing lanes, receivers that are wide open, screens and check downs that turn into big gainers...it gives a false sense of how "good" a QB is.
It seems that Goff is lacking in many of the nuances that separate the different levels of QB's. Elite, franchise, starter, potential starter and backup. Goff is teetering between that 3rd and 4th tier right now and it's all of those little things that are working against him. That extra little bit of accuracy to hit a receiver in stride consistently. Pre snap line calls and recognition. Processing and progressing through his reads. Looking off defenders. No one questions his arm strength but there are a lot of questions about the rest right now.
Some scoff at the idea of Goff "forgetting" how to play QB but I don't think that's quite right. I don't think he's ever really known how to play NFL QB, it was just masked by a unique set of circumstances for a short while.