When you have shulker what shot you and in same time you have command block(repeat) with command in it "execute @e[type=ShulkerBullet] ~ ~ ~ summon ArmorStand " , then bullet despawn without any real reason
MC-101625
Shulkers
Resolved
Invalid
0
It hit's the armor stand that get's summoned, when it slows down to make a corner.
Give the armor stand a marker tag, and it'll no longer happen.