I would also maybe try relaunching Mango from the command line and watching for any errors that occur when you try to view a watchlist that has this problem, if it persists through a restart.
The cron expression should be evaluated against the server timezone AFAIK (it uses the timezone from the OS/JVM by default, you can override this in your env.properties file).
Are you sure you don't have your server timezone set to UTC?
Ah okay. No deleting that class file is the beginning and the end of solving that issue (well, you probably already had to restart Mango) What slowed down?
One of the lowest hanging fruits to speed up a Mango is to change the database stream type in the env.properties file. Try setting
I also think that you just need to edit your point template and set Logging to "when point value changes". I don't think there's anything else you would need to do.