If you are running version 2.13.5, please update to this version and check your config values again.
Changelog:
Fixed a bug introduced in v2.13.5 that ignored "knockback.sprinting" values. This happened if the following conditions were both met: - The player was holding an item without knockback enchantment; - The value "knockback.enchantment.knockback-level.ignore-sprinting" was set to true in the config (which is by default).