My 650 (and my PCs) seemed to be having this same problem where the store wouldn't automatically update any apps on the last two insider builds. I reported the feedback and then went back to production builds on everything - I couldn't figure out a way to fix the problem and I tried for a while.
EDIT: I tried the build they released last night (14371) and it worked like a charm. I had the newest version of the store from the start, and it updated something like 25 apps after a hard reset.