How to debug whats happening when it looks like nothing is happening

Hi everyone, so I got a strange one here

How do I debug a webpage that looks fully loaded but actually isn’t, when all the network activity has stopped, and everything seems static, but the info that should be displayed is not, and then about 45 seconds later it suddenly appears.

If you feel like watching a very boring 1 minute video with no sound of my mouse bouncing around and a timer running, here it is. Im not overselling it when i say this video is boring.

is component a 3rd party api? ie not on your server? any thing in the console?

Its all on my own server, console has quite a few messages

14 Warnings about files missing

1 Error I am trying to figure out Bootstrap doesn't allow more than one instance per element. Bound instance: bs.tooltip.

52 AppConnect messages all saying [Violation] 'message' handler took 166ms polyfills.js:3

Maybe I need @Dave’s Mantis debugger tool

Edit: I think its the same issue as mentioned here

What is that progress that is shown in the video? It goes until 44 (about 75%) and then disappears and then the page seems to react again.

Its just the page running for 45 seconds where the page is totally unresponsive, can i PM you a login so you can check Patrick.

Basically the site loads, and all looks good, thats maybe the first 5 seconds, then it becomes unresponsive for 45 seconds, and then its perfect until refresh

Edit: Sorry not totally unresponsive, basically it just can not run any other server actions till the polyfills have completed, but I can still scroll the page and see all the loaded images, and the lazyloads carry on like normal.