PF1e
Shaman Spirits
Bones Spirit

Bone Ward Hex
Bone Ward (Su): A shaman touches a willing creature (including herself ) and grants a bone ward. The warded creature becomes encircled by a group of flying bones that grant it a +2 deflection bonus to AC for a number of rounds equal to the shaman’s level.
At 8th level, the ward increases to +3 and lasts for 1 minute.
At 16th level, the bonus increases to +4 and lasts for 1 hour.
A creature affected by this hex cannot be affected by it again for 24 hours.
The 8th level Duration Bump is only beneficial at levels 8 & 9. After that, the 1 r/lv is equal or better from Levels 10 - 15. I feel as though this must be an error. But I can not find anything about it online.

was wondering if anyone's Google skills are better than mine and might be able to find an answer. I can't say I have ever come across a spell losing power at a higher level like this (duration only).