Hi,
Encounter similar problem on 27 Mar UMP USM alarm view not updating with just around 300 plus active alarms .
Wait for 15 -25 mins to see a flash blue entry is the alarm view which indicates a update on the alarm view.
Had to close all not in use Infrastructure Manager Alarm List from other remote server and clear each browser cache.
Some browser cache accumulated to 1GB on my environment most problematic PCs.
Today check the UMP USM alarm view again and all open browser on 4 PCs seem to be updating 2-3 mins on accept and reassign alarm.
Regards
Guan Hua