I think n9revised's suggestions are good ones. I also think you should double check that your low power screen setting is correct (it may have been auto-switched with the other stuff you did). Go to Settings -->Device-->Display-->Standby screen (should be activated, if you want it).

There are other, better Twitter apps out there, if you don't want to reflash. QNeptunea has been mentioned, but Tweetian is also good and has swipe integration, too.

I would also check your search function (the magnifying glass app) and type in some of your contacts there. Sometimes the tracker can lose track (how ironic) of contacts, but the search function will turn them up.