|You said: The worksheet name is being switched to another worksheet.|
That is not what the links that you posted show.
I see 2 changes:
1 - The path has changed from 'O:\Investment Committee\Portfolio Performance\UST NAV\
'O:\Investment Committee\NAV Data Input\UST NAV\
2 - The specific cell referenced has changed from $H$21 to $J$21
The filename and worksheet name remained the same.
I don't have an answer, but have you looked in the 2 folders
(Portfolio Performance\UST NAV\ and NAV Data Input\UST NAV\) to see if the same filename exists in both.
I don't mean anything by this, but are you sure you are opening the same file each time? The fact that the path is changing but not the filename or worksheet name seems to indicate 2 files with the same name in 2 different folders.
Obviously I'm just guessing here, but that's what it looks like based on the links you provided.