Brought to you by "but why is my shared #Yocto cache corrupted when two machines build off of it at the same time" debugging sessions while #Bitbake actually uses locks (flocks :) ). This eventually got "resolved" by mounting a local NFSv4 and making the servers all use the cache over NFSv4 instead of one over ext4 (on the server the disk is physically connected to).
https://www.youtube-nocookie.com/embed/videoseries?list=PLW_oRrdNdnFknsXxy1LjNSpr3b2Fma_W5# #Yocto Demystifying the OVERRIDES
mechanism and #Bitbake operators #Y2021 : https://elinux.org/images/4/45/004-1325-SLIDES-demystifying_the_overrides_mechanism_and_bitbake_operators.pdf