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PA Desktop Loses Ability to Communicate with Browser After Server CPU Change

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Posted on by LucidFrog99

We need to scale down the number of CPUs on the Azure VMs used to run our PA Desktop flows. We've tried this twice now and we can't get PA Desktop to communicate with Edge afterwards. We get the following error in a post-update test flow that just opens Edge to the Microsoft homepage and then closes the browser.

Action 'Run_a_flow_built_with_Power_Automate_for_desktop' failed: Problem while executing action 'LaunchEdgeCloseDialog'. Failed to assume control of Microsoft Edge (communication with Power Automate web extension failed)
Microsoft.Flow.RPA.Desktop.Modules.SDK.Extended.Exceptions.InternalActionException: Failed to assume control of Microsoft Edge (communication with Power Automate web extension failed) ---> Microsoft.Flow.RPA.Desktop.UIAutomation.WebAutomation.Core.WebExtensionsBrowser.WebExtensionHostNotAvailableException: Could not connect to the web extension's native message host within the remaining timeout period (58 seconds). ---> System.TimeoutException: The operation has timed out.

Here are the steps we have tried:

Upgraded PAD to latest version.
Ensured Edge PA extension is at latest version and enabled.
Removed and reinstalled Edge PA extension.
Uninstalled and reinstalled PAD.

When looking at the following articles, there are mentions of making sure that the browser messaging is allowed to communicate with PAD. There are no policies blocking this, but I didn't try adding the reg key to allow PAD.
Failed to assume control of Edge or Chrome or Firefox error - Power Automate | Microsoft Learn
Troubleshoot issues in Power Automate browser extensions - Power Automate | Microsoft Learn

There is also mention of using WebDriver as an alternative. Browser automation actions reference - Power Automate | Microsoft Learn

This all seems so odd just because the number of CPU cores have changed! Has anyone come across this with a reliable fix?

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Power Automate Desktop

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KC Maringanti 30 on at

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We had same issue with Chrome browser. After all the analysis we found that Web Automation Native Message Host process was not starting automatically when the browser is launched. We tried upgrading the browser and PAD to the latest version and tried but it did not help.

Generally, we install only machine runtime on the VMs, but interestingly when we tried to install Power Automate Desktop as well it worked.

It is running smoothly from a month or so.

Hope it may help!!!

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LucidFrog99 52 on at

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Okay, this is embarrassing but the issue was with our testing flow. The step of the PAD flow that was failing opened Edge to the Microsoft homepage, then closed it. Apparently the homepage is kinda bloated (no, really) and the reduction in CPU performance was causing it to take slightly longer than before, passing the timeout threshold. Switching the test page to Google's solved the testing issue. The PAD server's been in production running fine thus far.

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KC Maringanti 30 on at

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Glad to know that you are able to resolve the issue. Thanks for sharing the RCA, it definitely helps us.

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