Hey,
We have started seeing a “Exception in changedobserve callback: Error: Unknown id for changed: [document _id]” error in our logs (hosted on Galaxy) from a cursor observer and is having a hard time figuring out why?
Everything in the changed callback is wrapped in a try catch that logs any errors to APM and the server console, but nothing is logged in relation to the error.
We have seen a steady growth in usage and the observer is currently looking at around 60.000 documents. The Galaxy app has not problem with memory or CPU usage though.
The error seems to come randomly and sometimes up to 5-10 times within the same millisecond (log example below) and only on a subset of the documents that change. We can’t find any pattern when looking at the documents that generated the error.
Does anyone know what exactly the error implies and could it be that the observer is simply overloaded?
If we are reaching the limits of what an observer can handle, what are the best alternatives?
Any input is highly appreciated
Thanks 
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: EuiBvDdSs4mPriefB
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:23+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:24+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:20:32+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:20:32+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:20:32+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:20:32+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:20:32+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:20:32+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:20:32+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:20:35+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:20:36+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:20:37+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v
2022-02-21 17:29:10+01:00 Exception in changedobserve callback: Error: Unknown id for changed: NwW6KY7KxfxbB6hyn
2022-02-21 17:30:28+01:00 Exception in changedobserve callback: Error: Unknown id for changed: qsmtNNFBztFm6f25v