I've always felt a bit of a weakness in the software is that if someone has you on ignore they have the option to still view ignored content, therefore they can see your posts but you can't see theirs.
Naturally this will often lead to the ignoring poster still being able to reference the ignoree's posts, without right of reply, which I find annoying. You can't return the 'ignore' because you can't see their posts.
I've discovered a solution that works, on a PC, not sure about mobiles. If you know the person that has ignored you, if you send them a blank message it will go through the system but they will not see it.
On the sent messages page however, you will see the message with their user name, hover the mouse over it and you can hit ignore which means they will now also no longer have the option to see your posts.
Thought that might be worth sharing.