Globals are session specific. So when a user logs in, the globals are reset to their state as when the file was put on FileMaker Server.
Without knowing what kind of data you're trying to share between users it's a bit tough to recommend an exact solution. Here are a couple of options....
Since you say the data changes regularly - don't use globals. Create a place to store the data, likely in another table, and create a relationship to that table. You're likely going to use the 'x' option on the relationship type. This will match everything (vs a 1:many or 1:1 relationship type).
Script it. Put a series of "Set Field" steps into a startup script and set the global fields that way. Less optimal, but it works. Relies on users logging out in order for them to see the updated values.
If you're using globals, you have to take the file off of FM Server, open it locally, change the values and then re-upload to FM Server. This will make the values stick (until the next time they need updating).
Thank you very much. Problem solved.