Have you enabled logging, e.g Application Insights? If you have, please check the logs for clues. Your information isn't suffcient for us to give you any pointers.

If you open the request in a new tab (in browser console), what does it give you? 

It says that ”page could not be open temporariry” @quanmai

No we dont hv insights @johan

apparently that's a custom error page, what if you disable customError to see what it returns? 

Hi Quan, pls ignore my last reply and see the preview in image attached at https://imgur.com/a/nEFUqZk

Is this a particular block or all blocks in general? The only way to resolve this issue is to find the "real" asp.net error message. The screenshot you have is a friendly error message and doesn't tell you anything about the real issue. You can ask Epi MS to turn on the logs so you can find out the details of the error (which is what Johan & Quan are trying to get to). 

there was an unhandled scenerio in a javascript on a page and once we altered code, it seems to now work now. Although strange that it worked before in prep env. Now i see unexpected token error but everything is working. But console errors are not my friends, i need to get rid of them.