I suppose it was inevitable, but I finally had a failure-to-fire shooting my relatively new R9s. Happily there was only one in 28 rounds -- and the second strike did the trick.
The problem cartridge was a Federal Premium LE 124 grain H-S round -- from a newly purchased box of ammo. Seven "old" (pre-shortage) Federal Hydra-Shok 147 grain cartridges fired before the FTF worked fine, as did seven "new" Gold Dot 115 grain rounds and seven Win WhiteBox 115 grain FMJs (all fired later).
Assuming I recovered the right casing, the primer strike looks mighty shallow, which might point to a hard primer (supposedly unusual for Federal, but maybe a "feature" of their Law Enforcement ammo).
Also ... I don't know why, but the Gold Dots definitely felt hotter than the other rounds.
I guess I'll go with Gold Dot 115 grain like so many others.
Ron