Different number of modes while performing the EEMD (Ensembled Empirical Mode Decomposition)
It depends on both on the signal content and on the EMD implementation. EMD can be sensitive to time shifts, especially with strong transients, to noise power. Robust or constrained EMD on single signal or multivariate signals have been developed.
Your question relates to signal morphology, processing purpose, and quality metrics. I doubt they can be answered globally.