In the latest beta, the ore distribution has changed. However, the gold ore, which now generates between y=-64 and 32, no longer generates its deepslate variant. This causes the gold ore to fail to generate below y=0/on -y layer.
This is most likely because the replace_rules doesn't include the deepslate block to be replaced by.
Step to Reproduce
1. Try to clear up an area in a cave below y=0 using these commands.
/execute @p ~~~ /fill ~10 ~ ~10 ~-10 ~-30 ~-10 air 0 replace deepslate
/execute @p ~~~ /fill ~10 ~ ~10 ~-10 ~-30 ~-10 air 0 replace tuff
2. Put these commands into the command block, and set it to repeated.
3. Try to find if there is any gold generating there.
There are deepslate gold ore generating down below y=0.
No deepslate gold ore generating at all below y=0/negative y.