Legal Question in Real Estate Law in California

You mean for the same dwelling unit? At a minimum, the landlord is supposed to file and serve a Notice of Related Case and list the related case on the subsequent pleading. You, the tenant, could file and serve a Motion to Consolidate on five days' notice. Look it up in Rutter Group California Civil Procedure Before Trial, Chapter 12. At any hearing in one case be sure to bring up the other case. Accuse the landlord of "judge shopping" (which is what the landlord is doing).

It's especially suspicious that judge-shopping is involved if (a) the first case was assigned to a particular judge and is then voluntarily dismissed by the plaintiff, and (b) your county or district within the county is large enough to have more than one judge doing UD cases.

In answering this question, I am assuming that the first UD case is still pending. If the first UD case is still pending, you should answer the second case with a motion to consolidate, and bring it to the first judge's attention. It certainly looks like forum shopping to me, and the first judge is not going to be too happy when he or she gets wind of it.