skiboot 6.0.21 was released on Tuesday Jan 7th, 2020. It replaces skiboot-6.0.20 as the current stable release in the 6.0.x series.
It is recommended that 6.0.21 be used instead of any previous 6.0.x version due to the bug fixes it contains.
Bug fixes included in this release are:
npu2/hw-procedures: Remove assertion from check_credits()