If you use Apache httpd in your network environment, where you route ImageMaster requests through, you must not use the Apache “prefork” multi-processing module!
This will repeatedly block the client for end users, giving the impression that the client got stuck. Instead, consider one of these solutions:
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Preferably, configure “event mpm” [Apache MPM Event].
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Try to tweak the H2MinWorkers [Apache H2MinWorkers] (on your own risk, however).
Rationale
ImageMaster uses the HTTP long polling strategy to handle background requests that take up to 60 seconds. According to [Apache MPM Config]in prefork mode the internal module “mod_http2” will only process one request at a time per connection and other requests will stall. Prefork is an outdated strategy that is only chosen if you run processing engines that are not prepared for multi-threading.