After a Windows update, blocks are seen on powershell files with a __psscriptpolicytest suffix.
These files appear to be related to the OS attempting to check whether or not AppLocker is enabled, based on the contents of the .ps1 files seen thus far.
According to this article: Applocker, Windows 10, audit warning PS1 script , these files are created by App-V when syncing published apps upon login, and the files are then deleted afterwards. Since then, it appears that the files are used in more cases than only when App-V is installed, and seems to be a 'normal' part of Windows 10 operation.
The article also suggests that this was a "known issue" in 2016/2017, and that Microsoft renamed these scripts to use the __psscriptpolicytext prefix in order to allow applications such as Cb Protection to allow these to run based on the name.
If the desire is to allow these files to execute, a rule would need to be put in place to allow the following:
Many customers are also choosing to block these files. The sample rule listed below shows a method of allowing these to run, however security concerns for your specific environment should be taken in to account when deciding whether or not to allow these to run, or whether to create a block rule for these.
If you have older versions of Windows 10 (pre Creators edition), please read the Additional Information below for an extra path needed.
A screenshot of a sample rule is below...
Please note - the __psscriptpolicytest naming convention is used by Microsoft in Windows 10 versions of Creator and above. Older versions of Windows 10 use a more random naming convention (8 characters dot 3 characters dot ps1), so the following line would need to be added to Path or File section to account for these older versions:
As a general rule, if you are getting these blocks after recent Windows updates, you can look at the path and naming convention of the files you see in your environment, and adjust accordingly, however the two paths mentioned in the resolution, and this additional path here for older Windows versions should resolve the blocks for most customers.