app not running on a specific computer

We are deploying/testing a new shiny app. We have found two computers that lock up when we go to a specific tab in the app. The same behavior occurs whether we run the app natively on the computers or run it via server over the web. No errors are logged in the logs/console either way. On these computers with problems, the app in essence spins its wheels indefinitely (can see high CPU usage). The odd thing is most similar computers do not have this behavior and run the app fine when this tab is selected.

Without getting into all the reactive code that may be in play, does anyone have general advice about why things would run fine on most PC's but have problems on just a couple machines? We get the same behavior in different browsers (Chrome, Internet Explorer, and FireFox)? Any help figuring out what makes these specific computers have problems with our code would be greatly appreciated.