Over the years I have found that the update of balance is frequently out of date but when I go to do the math it does work out if you go back 3-4 transactions. This does not mean there is not some nefarious Starbucks balance vampire drinking off of your rounding errors.
I also find if it does not bring up the option to tip then there is usually something messed up in syncing the account to the app. Usually a log out and back in fixes it. Sometimes it is just a mess that does not resolve.
