https://www.whatifsports.com/HBD/Pages/Popups/PlayerStats.aspx?pid=5034976

The 7 negative plays seems like an outlier given he had ten in 120 games last year and his ratings did not move much (dropped a point in range).

https://www.whatifsports.com/HBD/Pages/Popups/PlayerRatings.aspx?pid=4818161

i assume the culprit here is the insufficient arm strength?

Im trying to decide what, if anything I want to do about this (I have two other decent corner of type bats that are platooning currently). But when I compared my team defense to other teams, then see 13 - plays between these two, it was definitely a little jarring.

You can see the source of the negative plays by going to the game log screen on the player card, then click the "view" for boxscores. For the RF, looks like they were all bloop singles which I assume would be related to his range rather than arm. There a few other guys in your league with similar negative plays, some with 70+ arms.