Unfortunately this is still a known issue and is related to a recent browser update and not actually from an issue on the Keap servers or with your app. The newest browser releases are supposed to fix this issue but haven’t been released yet. In the mean time, there are some things that some are reporting success with.
This is a memory related issue so anything that lessens the use of memory is going to help avoid it. So closing all other programs on your computer and only having one browser tab open reportedly does some good.
Trying different browsers may help as some browsers make a less demanding use of memory as others do.
Reverting to a previous version of the updates for your browser (The previous version I believe should do it). As this is most commonly presenting in google chrome browser, here are a couple of links on how to do that.
I’v had some luck with placing the email icon on the canvas, then REMOVING the line that is automatically created to that icon and finally backing out of the campaign so it saves the email icon in place and then I have been able to go into the email to edit it. BUT, this only works the first time so make sure you get all the editing you want done on the first try before saving or backing out of the email editor.
Further updates and info can be found here: