Inserters have a strange moving pattern when low on power and on a non perfect circular swing as can be seen in the following video. As far as i can tell this happens only on extending/shortening (lateral?) movement. Could be also caused by Bob's inserted mod. The same inserter works totally normal when fully powered.
https://youtu.be/Wehhjp6SRu4
Might not be the worst bug currently, but still its there for your testers to increase coverage

Btw: Your Team is as totally awesome as your game! Keep up the wonderful work. Cant wait for the next FFF. As a Software developer myself i really love your details about the development!