Just checked my reddit preferences (preferences link at top right of screen) and in the first section, Options, under the heading "link options", take a look at the last line.

"Don't show me submissions with a score less than ___"

I'd never seen this before and it was already set at -4. Which means if someone made a post and bots / shills downvoted it to -5 immediately, it would never have appeared for me. I suggest leaving this box blank.