We have upgraded our application recently from CF10 to CF2018 Update 5. Apart from the JS library changes, we are seeing performance relevant issues. The time to load has increased exponentially.
e.g. the ext-all.js is taking around 10-30 secs to load on different servers. Even a simple image would take 2-5 secs load.
If someone could help me here.
Thanks in advance
You're asserting that it's CF making js and image file downloads take longer. It's possible (indeed likely) that CF is not involved in serving those at all.
And you mention being on update 5: just note that there is now an update 6 since a week ago, and most people should update to that to resole problems they had due to update 5. Note as well that you should update the web server connector as well, though again I doubt these would help with the problem you are reporting.
Let us know what you find.