What do you mean with "compress"? Does it relate to image (file) size or are you rather referring to dimensions (width/height)?

the exception trace will contain more information what exactly failed, and the error messages are normally quite helpful.

The most obvious reason for such an event handler to stop it got blocked because it took too much time. The OSGI implementation blocks event handlers which consume 5s of execution time per invocation. That means if you need to more complex operations or even external calls, you should delegate that ...

It seems that you want to override the exporter for the v3 page template of the Core Components. And most likely there is already one for it, and for that reason it's not working. I would recommend that you define for your own pages a dedicated resourcetype (you can define the v3 page as supertype) ...

You cannot with ootb tools. As the CRX Explorer (CRX DE as well!) operates in its own HTTP context, Sling authentication cannot be applied to limit access to specific paths or features of it. When you are authenticated to the repository, you can use all the tools of the CRX Explorer according to the...

If this is AEM CS, it means that the AEM CS instance is not responding in time to the request, and that could have a number of reasons. The most obvious is that the AEM instance is overloaded.You should raise a ticket, so support can look into the specifics if this situation.

In AEM CS you cannot use content distribution or replication to get content from publish to author; this pattern is not supported.

Check https://sling.apache.org/documentation/bundles/servlet-helpers.html, it explains the tools Sling provides for this.

No, that API is still working as it is on AEM 6.5