Thanks for the workaround @kborowinski . The actual issue is caused by the fact that for every progress change a new ProgressRecord instance is created?

I have published 2.4.1-beta0008 including your fix.

@thoemmi During the test I've found that higher the number of ProgressRecord instances, the more often NRE is happening. So that's why I've refactored the code to reuse the ProgressRecord. It substantially limited the number of NREs, however they are still happening sometimes, and hence temporary workaround that swallows the NRE in try {} catch (NullReferenceException) {} block.

What keeps me wondering is that NREs are not happening on PS 5.1 at all. Also the NREs are occurring mostly on ProgressPane completion, i.e. Microsoft.PowerShell.ProgressPane.Hide(). It almost looks like occasionally the completion is happening twice.

I do believe that this is a race-condition in PowerShell as similar issue is open already (PowerShell/PowerShell#17497). There was a PR for it, implementing extra locks, but it's closed now (PowerShell/PowerShell#17498).

I remember 12 years ago when I started 7Zip4Powershell, the main challenge was that 7zip raised the Compressing event in multiple threads, which Powershell didn't like. Therefore the peculiar ThreadedCmdlet implementation 🤷‍♂️