2. The bugs causing the system to fail are... actual bugs
The first episode is all about flies. In the first sequence, we see a fly land on the actual eyeball of a host. We're told that the hosts literally "can't hurt a fly." And then, of course, the final scene involves Dolores swatting a fly and killing it, proving otherwise. On top of that, DiscoverWestworld.com, which is incredible and set up to act exactly like an actual booking site for Westworld, includes a Terms of Delos Destinations document, which has a crucial line mentioning that all livestock within Westworld are hosts, "with the notable exception of flies."
So... the flies are real, but no other bug is real? Notice that the document doesn’t say "insects" or anything general; it makes specific reference to flies. And because flies don't act in a predictable manner, they can literally serve as bugs in the hosts' operating systems, perhaps triggering the robots to rebel. Some theories speculate that Ford or Bernard introduced real flies into the system and entered code that triggers the robots to rebel once they interact with the fly, but I'm not sure. We saw Madam Maeve react more to the trigger words "These violent delights have violent ends." Nonetheless, the flies do seem to represent a literal bug in the system, a drop of chaos that will eventually cause total mayhem.