Wonder Nishii dropping leaves

[Mandomaniac]

Worried about my Den. Wonder nishii developing yellow leaves which then dry and drop off.
This is occurring on the smaller canes. Canes then yellow, but are dry, not mushy.
No 'ring' noted as mentioned in another thread.
The larger canes and leaves still look green and happy.

Repotted this plant not long ago.....it was severely rootbound and a number of roots were dead and removed.

Is this something to be concerned about or simply 'normal'?
My other orchids (catts, onc, dtps, b, vasco, etc) all doing well...but this is only den I have.
Quite new at orchid culture, and admittedly hooked, but still stumbling my way along. So....guidance is appreciated!

Thanks for any advise.