Concurrent Requests:
"A job that exceeds its number of concurrent requests doesn't terminate. For example, if you export three pages in an A1 SKU, the first job will run, and the latter two will wait for the next two execution cycles."
Note that concurrency also applies to pages within a report. So a single report containing 20 report pages/tabs will not complete until each one is rendered individually. How fast this is will depend on the capacity size.
Embedded Capacities:
You need to have the reports hosted within a workspace that is running within an embedded capacity.
The larger the capacity... the more reports you can run concurrently, plus (in theory) your reports should render faster due to the increased CPU and memory.
It could be the case that whilst this feature is in preview, it is running slower than it otherwise would normally?
It's worth testing it with a larger capacity to see if this makes any difference.
You clould also check if your report contains too much data and complex report definition. Also check if the network is under heavy load. You can try to clear the cache of web browser. And re-publish the report to service for a test.
