Email builder item disappearing

I’m trying to use dividers in my email. When I drag the icon onto the email it doesn’t show.
The divider is there and I can drag it around but it isn’t visible, the colour the divider is set to doesn’t seem to matter.
I’ve tried to delete the email and start again but it still doesn’t work, this problem seems to occur periodically. It’s not every divider that disappears but when I delete the invisible one another becomes invisible.
Has anyone experienced this? or found a fix?