Vitor, if you zapped from Minibits, check the error detail on the related transaction screen. 

Failures are either network, lightning or wallet state itself. Expand the audit trail params to find out.

e.g. I have reports (could not yet simulate on dev device) that transaction did not fully complete in case user fired many zaps at once. Seems like android might supress too heavy background processing - resulting in incorrect wallet state that breaks further zaps until cleared.