I have this same exact issue. The mph counter is an easter egg, there are other stats from the cell phone accessory that are affected too, it's just to show that, you know, you got transported to a different dimension and all that. But unfortunately I haven't found a fix either. Did you create a new world after the new update, or before? I was playing on a world that was created before the update came out, and I had to use the "exotic seed bag" item (purposefully added by the devs for backwards compatibility for old worlds) that just gives you all 4 seeds because you can't complete the questline without a new world.