Same problem. This is the first thread that actually matches up to my problem exactly. The symptoms are a perfect match, and I didn't even think to check my save files at all, but it's the same issue with saves that are 8,192KB or larger. At this point, my most recent working save is 8,191KB, so I'm largely stuck from progressing unless I find a way to reduce the file size.
I reached the point of no return maybe 30 hours in, turned away and started doing everything else I could. I never went back to finish the main quest. I periodically delete saves that are extremely old, but I had held onto maybe the previous 10 manual saves just out of paranoia for things like this.
My most recent save file's playtime is 68:44, this is the one at 8,191KB. At this point, my oldest save's playtime is 63:32, and it's 7,515KB. I know I was running into this problem earlier than that, but it's the only save I have under 8,000KB. Pretty much anything I do after loading that save causes it to jump.
I've been running into this problem for 3 days, and since it started I've been trying to look up what might be causing this but nothing else matched what I was seeing.