Same thing just happened to me at the UA forum, it's about an expiring 10% coupon, I read the rules and want to be polite so I make a thread stating that I know I'm not at 90/90 yet and ask whether sending that in PM is ok, it disappear within 15 mins w/o any explanation. Seems a mod just took a look at the thread title, didn't bother to read the content and delete it.
I feel like I was trying to do the right thing and got a slap in the face instead...