Unusual errors on recent stable/13 22-Dec-2022

Hi,

I recently updated my package builder machine to the 
stable/13-n253297-fc15d5bf1109of (22-Dec-2022); and appear to be having 
some unusual issues when building with a high number of jobs. My package 
builder uses synth (which uses nullfs on ZFS), and I have had failures 
with missing files, as well as what appears to be sequencing issues with 
Makefiles. If I re-run the build, these errors usually do not reoccur.

I'm puzzled as to what is happening. Is this just happening to me? It 
appears that the ZFS code has been updated recently, and I'm wondering 
whether a regression has crept in. [Or it could just be my hardware?]

Cheers.
-- 
Jonathan Chen <jonc@chen.org.nz>