I have just posted in WIN10 OS Forum but it doesn't  appear in Topics I've participated in: All my other ones do!

Happened to me a couple of times,   i wait 5/10 minutes and it appears then 

My problem - finger problem :(

If you click on 'View New Content' you will have immediate confirmation whether your reply has (or has not) been submitted properly.

Wonder if this has got something to do with the fact that AVSIM recently was - and/or still is? -  under 'Performance Mode' as outlined here in #2:

http://www.avsim.com/topic/475658-view-new-topic/#entry3304533

 

However and as pointed out by olli4740 just above: Using 'View New Content' works.