Not sure but that could be because of network/machine related issues that the libraries take time to load & process. For the m/c where you notice the error, do they have local AEM or they use the same remote/cloud AEM server?
Couple of pointers to debug:
Check the page load time in network tab of developer toolbar or even in 'Developer' mode or use a plugin
Look for any errors/warnings in the console tab of developer toolbar or server logs
Try to find a pattern based on OS/Browser/network/memory/cpu combination