Can you show a screenshot / screen recording? It's supposed to launch %TEMP%\StartIsBack_update.exe
What is your Windows version?
Are you sure installer is not under some window?
Enable GDI and USER columns, check if there is a resource leak?
Enable 'command line' column, check if it's main shell or separate browsers leaking?
Try to find any noticeable explorer.exe memory leak scenario?
Memory usage should be sub-100MB.