Russian soldiers seem to have been complaining about shortages for some time now. Just look at how the amount of shelling has gone down. They're sending T-55's to the front line now. Even the Kremlin will have to acknowledge the reality at some point I guess.
Ukrainian soldiers are also complaining about lack of ammunition and are fielding. T-55s. While Russia has a much larger geographical and raw resource base to rely on to build new Equipment, Ukraine does not have that luxury (but does have western support). So if Putins statements about increasing production of military equipment 3x-10x are accurate projections, I can see why they still think they can keep going.