Yeah, the datasheet & especially the footnote for CL(itg) is confusing & misleading, it should be rewritten :!:
Maybe best to check these NXP Application Notes:
https://www.nxp.com/docs/en/user-guide/UM10301.pdf
https://www.nxp.com/docs/en/application-note/AN10652.pdf
Cosco has 25pf built inside the RTC, so no need for C17. Remove it.
Keep C16 for Cosci. With 25pF, you should typ. reach 12,5pF load.
Considering StrayC, PinC, BoardC and CapTolerances, you may need to do finetuning on C16, to get the needed clock accuracy.
With this, your circuit should run.
If osc. still doesn't start, or drops, it may be an issue with Oscillator margin mismatch. For this case, come back here again.