First, let me start by saying you’ve made some beautiful tools. I’m really excited about the potential for integrating these into the product I’m working on.
So I’m working on a prototype for and integration with your viewer, and have been seeing the attached failures frequently. I wanted to make sure it wasn’t my code, so I took the example from GroupDocs · GitHub and tried uploading using this as well. I’m still seeing the error at least half of the time I submit a file. I’ve been trying mostly with various PDF and DOC files, and have attached an example PDF on the chance that the files I’m using have something to do with it.
We've managed to reproduce the issue that you are seeing and we're currently investigating, we aiming to have a fix ready for this ASAP. We rolled out a new production release last Friday which contained many optimisations regarding how documents are handled which looks like is has introduced some issues with larger files (instead of processing the whole document we now split the document into pages and process in parallel).
We've added some testcases so that we can trigger this issue on production, so once we track down and fix the root cause will be monitoring to ensure that there are no regressions.
These optimizations will also allow us to farm out individual pages for processing to allow us to scale GroupDocs alot easier.