On Aug 3, 5:58 am, wrote:
I covered the gaps in my underlayment and filled the hold with a "gray"
leveling compound that I mixed with water.

It doesn't say do, but I'm sure one of the ingredients is good old Portland
Cement.

This is a kitchen and I worked around the supply pipe for the sink, etc.
Right now the compound is against the copper pipe. Could this cause some
problem down the road?

Could, probably not in the lifespan of a kitchen. It could also
create squeaks as the copper moves, which would also tend to scratch
the copper. Generally it's a good idea to use sleeves fill the gap
with something that conforms to the firestopping requirements.

R