For answering my own question: After a lot of tests, we saw that the problem was more frequent on older devices.
By reviewing the components, elements and doing an extense memory research, we discovered that this actually has to do on how Android manages Applications and the memory.
If OS decides your application is consuming too much memory on the background, it's able to remove it by any time. No matter if it's executing an Alarm or not.
With devices with more memory (newer devices), the problem just disappears.