Hi! VSF (on Aruba 5400R zl2 Switch series) requires that VSF Link Interface's member ports are either 10 Gbps or 40 Gbps (not a mix). 1 Gbps ports were/are not supported.

Since there aren't pure 10 Gbps (SFP+) modules with more than 8 ports (and, generally VSF Link would be made using such ports of those SFP+ only modules using DAC Cables), I strongly doubt the 23rd port of a Module (made of 24 ports) port can be a 10 Gbps one [*]...so the one you're using is probably a 1 Gbps port...thus not suitable to be a VSF Link member port.
[*] Apart if you're trying to use 20x1G (BaseT) + 4x10G (SFP+) ports Module with SKU J9990A or 20x1G (BaseT) + 4x1/2.5/5/10G (BaseT) ports Module with SKU J9991A (provided that Smart Rate port(s) negotiates at 10 Gbps and not at lower speeds).