I have seen and caught many browns in rivers during their fall spawn run as far back in my youth as I can remember , maybe 20 years.
I can't comment on recent years though because trolling in the lake is mostly what I do.
In the spring I have caught them trolling in 10 fow with stelth presentation, long lines etc. preferably where murky water meets clear water.
As far as your observation of poor spawning numbers...good question!