I have this problem too, and hadn’t used a class statement.
I’m not very technical, so I’ve been writing any tables code in notepad and then pasting it into the wordpress editor.
If I reopen that post, it all disappears again, so if I’m lucky I kept a copy of the code on my computer and can repaste it. Otherwise, bleah!
The issue occurs with both posts and pages, so it looks to me as though the problem is with the editor platform.
Has anyone else been experiencing this problem?
Has anyone any input?
Thank you,
Jane