Thanks for providing the details.
It is important to inform you that prior to version 19.1 of GroupDocs.Viewer for .NET, the cache for a particular document was updated whenever the last modification date of that document was changed. This happens when you modify (and save) the file or when you replace the file with another file that has the same name but the different modification date. However, since version 19.1, the API no longer tracks the last modification date of the files and caching is done only once when the document is rendered for the first time. The cache never updates until the user updates it by himself. This change is done to reduce the number of calls to storage and improve the performance of the rendering when the caching is enabled.
In your case, a user may modify/update a particular document at any time and if the document already has the cached files, the API will fetch and display the previous version (cached content) of the document to other users. Therefore, you will have to implement your own logic to detect if the original document is modified or not. If it is modified, you will first clear the cache and then render the document, otherwise, you will simply render the document and get the cached content.
We have also prepared this sample console application for you to demonstrate how you can detect if a document is modified and then decide whether to read from the cache or regenerate the cache to get updated content. Hope it helps.