I don't know if I'd say YouGov is biased against Dems as much as their polls are just really erratic and often cut against current conventional wisdom, partially due to their large sampling period. Their results can be lagging compared to most polls.
Like I said above, their most recent wave actually favored the Dems overall, despite the first two favoring the GOP. Regardless, I try not to take them into account at all when thinking about the standing of a race. Since we're almost in the final week of the election, that'll be even easier to do as more polls flood in.
