It would be really helpful to see if there are any errors in your browser's Console when this particular error happens.

You can access the Console with Ctrl-Shift-J. 

You can also access it from the Browser Menu (upper right corner of the window) > More Tools > Developer Tools 👇 

It's most effective if we can capture only the errors as the issue occurs.
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The best way to do this is to clear the Console by right-clicking in the Console > 'Clear console' as well as showing errors only 👇 

and then try to replicate the issue. This gives us the best chance of capturing the exact error that's occurring. 👌 

If you could take a screenshot of any errors you see that would definitely help us get to the bottom of the issue quickly. The errors will be in red.

Thanks!