The same situation here, a big project (200ish tracks, 10 busses) runs to the limit, but OK in Cubase 12 with 512 buffer size, but playback will not even start when open in Cubase 13.
Disabling a few heavy plugins will allow it to start playback, but extremelly stuttery and crackly. The thing is that CPU is not even close to the breaking point, hovering around 75%, but ASIO guard fluctuates and spikes like crazy, in a manner that I have not seen before, not even in the early days of C12.
Also, my template opens and feels pretty smooth in C12, being built and balanced to behave well at 512 buffer size, but when open in C13 it feels sluggish, slow and crackles when trying to play midi.
I run it on Win 11, Ryzen 3950X, 64Gb, M2 sys drive, all SSDs.