Small wonder the ceiling is cracking! It’s not the original ceiling that was plaster on wooden lath. This ceiling is 3 to 4 inches below the remaining wood lath. The plaster is attached to an expanded metal lath. I cut some holes to discover this. Thinking the 3 to 4 inch gap meant 2x4’s had been sistered to the original joist for support for the newer metal lath. NOT SO. I have probed many feet with a plumbers tape in all directions of several widely spaced holes. There appears to be no connection between the new ceiling and the framing. All I can find are places where strips of the original wood lath has been pulled down and nailed to the metal lath. See picture. The pulled down lath strips seem to have no connection to the original framing. First picture shows a wood lath atop the metal lath/new plaster taken from below, and the second the same wood lath with a long nail attaching the metal lath. You can see that wood lath strip missing from the joist above it. WT Heck? This makes no sense to me. Was expanded metal lath with plaster so rigid it needs virtually no support framing? Tom?
Last picture shows the top of the newer plaster down through a crack where you can see bits of the metal lath