A single Unattended Robot cannot run the same background process multiple times in parallel on the same machine unless you assign multiple Unattended runtimes/licenses. With only one runtime, additional jobs will queue.
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No, you cannot run multiple background services at same time on same machine using 1 license.
You can only run 1 foreground and 1 background process at the same time on same machine from 1 set of credentials but that also requires 2 license. 1 license per parallel execution.
Yes, a background process can run multiple times in parallel on the same machine, but only if you have multiple unattended runtimes available for that machine.
Even if Starts in Background is enabled, UiPath will queue jobs when there is only one unattended runtime. One runtime = one job at a time. To run jobs in parallel on the same machine, you need to assign more unattended runtimes to that machine in Orchestrator.
So the queuing you’re seeing is expected behavior if the machine has only one unattended license/runtime. Once you increase the number of runtimes, jobs should execute in parallel.