Yes. I once lightly tapped my brush against the corner of a nickel plated
thumb tack and every sheet I coated had bad streaks. I don't know if
your problem would point towards something like this, but it is a good idea
to use a brush without any metal parts. The highlights are fogging? Are
you getting solarization in the shadows? Are you positive that the solution
is 20%? How are your negatives? Are they dense enough and have enough
contrast? It seems that silver-nitrate is a pretty forgiving chemical (much
more so than ferric oxalate anyway.) I'd look for the problem outside
of the chemistry.
Adam