I've tried to overcome the problem with fiddle~ and sigmund~ by looking for some pitch tracking solutions that don't use fft (as - if I understand correctly - this is whac causes drops in Bela). I've found the helmholtz~ external http://www.katjaas.nl/helmholtz/helmholtz.html#download which works really nicely on pd-extended, but I've run into problems trying to install it on Bela (trying to find out how to solve it on another forum thread). Anyone out there ever succesfully used it on Bela?
Another idea was to patch my own pithc tracking solution, which I eventually did in the very basic technique of zero-crossing - this works not so bad, but is far from perfect, and much worse than any of the three aforementioned modules.
This is really an issue for me and, for all the good stuff that Bela represents, I'm considering moving to another solution, i.e. Blokas Pisound (a Raspberry Pi audio cap), which seems to handle sigmund~ just fine... Still, Bela mini is much smaller and handles analog ins and digital outs in a much more straightforward way...