  Long-distance transport of spin information in insulators without long-range
magnetic order has been recently reported. Here, we perform a complete
characterization of amorphous Y$_3$Fe$_5$O$_{12}$ (a-YIG) films grown on top of
SiO$_2$. We confirm a clear amorphous structure and paramagnetic behavior of
our a-YIG films, with semiconducting behavior resistivity that strongly decays
with increasing temperature. The non-local transport measurements show a signal
which is not compatible with spin transport and can be attributed to the drop
of the a-YIG resistivity caused by Joule heating. Our results emphasize that
exploring spin transport in amorphous materials requires careful procedures in
order to exclude the charge contribution from the spin transport signals.
