I suspect that this issue is being caused by a plugin conflict and as such I would recommend that you temporarily disable all your non-toolset plugins and try again.
Once you have done this please let me know the results and we can move from there.
i have tried both with Firefox and edge and i get the same behavior.
did you try the custom post fields or the default fields?
i ask as the issue happen only with the custom post fields i created. see enclosed image and let me know if you tied with one of those fields.
just a small update that the issue might be related to the them.
when i change the theme to "Twenty Sixteen" adding the custom field works. when i revert to Divi them the issue is happening again.
not sure how to proceed from here.
please advise,
thanks,
I was able to replicate the issue and made a report to our 2nd tier team .
Hopefully there is a solution for this soon. However you can disable to divi integration and then add the fields and re-activate it once the fields have been added.
I know this will cause some inconvenience but this is the only suggestion I have until this issue gets resolved.