Fast advances? Who is talking about fast advances?

What is happening is almost trench warfare. Ultra-slow front advancement, ultra-high casualties.

Now, maybe what you mean is when Ukraine has successes they are rapid and wide ranging like the Donbas counterassault about a year ago or the Kursk incursion.

But Russia has advanced only about 30 miles in the last year, tops. All while going through multiple rounds of conscription, mercenaries, and now North Korean shock troops.

The ultra slow front advancement combined with massive numbers of poorly trained conscripts means: really high casualty rate for the gained territory.

My sources are generally the UK media. TimesRadio is pretty rah-rah Ukraine, but other sources generally back up the fundamental claim:

Russia is lose 1000-1500/day to gain really small amounts of territory. For russia to win they'll need to progress another 200 miles, which at this rate means 2-3 million dead russians or more.

Russian advances are enabled by artillery shells. If the artillery losses mount and production issues appear in shell production, then suddenly the Russian ground forces will be sitting ducks and Ukraine will counterattack very effectively.