Here's my situation with Lightroom CC, which didn't happen in previous versions.
I export a RAW picture using a defined export preset with a Photoshop action to automate processing in photoshop and then add the new psd back to the catalog as a stacked item. This works as expected.
If I click on the psd in the stack before photoshop has finished processing and saving the image, Lightroom updates the preview of the PSD with a view from the initially created PSD and not the processed PSD.
If I then move away from the image in question by selecting a different image and then reselect the PSD the preview is not updated from the updated PSD.
However, If I let the process rerun without selecting the newly created exported PSD and wait for Photoshop to finish processing and saving the file, then the correct preview is shown.
In previous versions of Lightroom, the previews would just update if the file has been changed.
Now if this occurs I have to quit Lightroom and reopen it to refresh the Previews of the files that have changed.
How many files are you exporting at one time and what pixel dimensions are the PS Action processed images returned to LR? When exporting and then applying a PS Action to a number of high-resolution image files it can take quite a long time to 1) Save the files in PS and then 2) rebuild the previews in LR.