My emails started disappearing recently too. Emails were being filtered to the "Social" or "Promotion" folder instead of going to my inbox. I checked my account settings in my panel and found that this filtering was turned off on the domain level and at the individual email address level. Despite this, emails are still filtered to these folders.
I contacted support via Chat. The Dreamhost rep told me that, yes, the new spam filtering system was causing these emails to be sorted to these folders even though I had the setting turned off. They tried to convince me that not respecting how I or my users wished to manage or sort my emails was actually a benefit to me.
I can potentially understand the need to filter what are perceived to be Spam emails. However, I do not think Dreamhost should be deciding to sort other emails. If you have an option for this in the panel, they should respect the choice and allow users to turn off this "feature".
I have been with Dreamhost for over 12 years. Unfortunately, I think it's time to find a new host.