After experiencing a huge spike in traffic, I suspected ghost referrals. So, similar to this recommendation (Google Analytics referrerless ghost direct traffic) I took a look in Google Analytics under the Technology > Network > Hostname report and saw that the vast majority of the traffic has a hostname equal to my domain (example.com). All good, right?
However, when I switched the report to show the service providers, almost all of this traffic is coming from service providers "amazon.com inc." and "amazon technologies inc." with bounce rates higher than 97%.
I thought, hey, maybe this is actually referral spam, but under the Acquisition reports, the traffic is almost all "organic" and "direct." The typical solution to ghost referrals is to filter in only valid hostnames (see here https://stackoverflow.com/questions/29717151/why-are-porn-sites-appearing-in-my-google-analytics-data/29717606#29717606), but what do you do when the valid hostnames are correct?