Resolved - On Friday we broke how our JS SDK files were being hosted which caused data loss.
We fixed the issue on Monday.

Who was affected?
Customers using our JS SDK via the snippet (https://developers.amplitude.com/#installation).
Customers who use npm to include our SDK won't have been affected.

What happened?
We had intended to increase the HTTP header Cache-Control max-age on all SDK files.
But we accidentally dropped and overwrote other important headers (Content-Type and Content-Encoding) in a way that broke how browsers loaded them.
We fixed the issue by re-setting the correct headers.

When did this happen?
We broke the SDK file headers at approx 16:45 PDT (23:45 UTC) 2019-10-18.
We fixed the headers at approx 09:30 PDT (16:30 UTC) 2019-10-21.

What are we doing to prevent this ever happening again?
At a low level the issue stemmed from us not understanding how boto2's set_remote_metadata method worked (we use AWS CloudFront and S3 for our CDN).
We at least know not to use this API in the future.
We'll also spend some time thinking about how we can tighten up controls around the SDK files to prevent similar accidental changes in the future.
Oct 18, 16:30 PDT

Resolved - The data processing system responsible for our Export API has completely caught up and our Export API is working as expected. All our other systems were operational throughout this incident and no data was lost.
Oct 14, 04:48 PDT