An observation about my FX-9, Shot flawlessly until I purchased 2 Spare SGM magazines. This is where the problems started (ftl fte) Eventually I discovered that the ftl issues were cause by the feed lips on the mags all being different sizes. A set of Calipers and a Channel lock and the ftl went away completely. I still noticed the odd fte, i disassembled all of the mags and learned the first mag was pinned under tension from the bottom, and the two new ones were under tension from the top (making the spring weaker and the bolt hold open not working). After this, everything is running perfectly.
When I was describing my issues to FO to try to find a remedy they told me I may need a bolt update of some sort, this doesn’t seem to be the case for now.