
Now pipes freeze at 32, so that is a pretty outrageous amount of manadatory wiggle room --23 degrees. I honestly don’t know enough about plumbing or insulation to suggest a fix
If the inside of your apartment is at 55, and the outside is at 9, and the insulation between the pipes and the inside/outside is equal, that puts your pipes at 32. In theory the pipes should be “closer” to the inside temperature, but plumbers don’t always put pipes in with an aim to avoid future plumbing work…

If you don’t run any water overnight then turn on the cold tap (preferably first thing in the morning) and take temperature readings as it runs, you can (likely) spot if you’ve got any cold spots / weak insulation against outside cold, assuming it’s a lot colder outside than inside that night.