3216 refusing buffer changes

Neither from within the app, or the interface’s control panel, can I change the ASIO buffer from 64. I’m stuck! No other values other than the current one is available in Cantabile’s dropdown.
I went back to 3210 and all works. Switched buffer to 256.
Reloading 3216 and the menu has recovered.
Set to buffer 64 and quit.
Reloaded and the menu still works.
Tried this a few times and it has definitely recovered - but perhaps symptomatic of some other issue?