Apparently Russia is running low on heavy artillery shells. They had 13 million shells (total, not just heavy) stockpiled at the start of the war, and have fired 10 million of them, with only one factory currently producing heavy shells, and they’re struggling to get the 2nd one online.
And keep in mind that just like the tank situation, the good ones have largely been used up, and what’s getting fielded now has been sitting on shelves for decades. Apparently a lot of misfires happening.
Unless they fix their production problems, soon they are going to have even more problems.