I just sent the following to on1 support. I thought it might help someone here. This is on my Late-2012 i7 iMac, 3TB Fusion, 32GB DRAM. The error is present with the graphics processor checked or unchecked.
====Sent to on1 support====
Executing an on1 9.5 premium module from Lightroom CC using the 'Edit In' function (accessed via a right click) causes the develop module of Lightroom CC to become unstable. This does NOT happen when the modules are accessed via File->Plug-in Extras.
Here is an example on how to re-create the problem. Automatic writing of XMP data should be turned on in LRCC.
1. Enter the develop module of LRCC.
2. Select a JPEG file.
3. Right click and select Edit-in and select Perfect Enhance 9 Suite.
3.a. In the dialog box select Edit a copy with Lightroom Adjustments
b. In the Copy File Options Select PSD, ProPhoto RGB, 16 bits/component, Resolution 300.
c. Select Edit
4. When the Enhance module has opened select Normal Photo from the pop-up.
5 Select Favorites, on1 - Auto Levels
6. Select Apply
7. Upon return to the LRCC develop module begin editing the photo just returned by adjusting the develop sliders. Very soon the display will flash each time a slider is moved. The flash does not always happen everytime a LRCC develop slider is moved, but happens very often.
Apparently LRCC has been put into a mode where it re-writes the XMP data in a loop when the sliders are moved. One can confirm this by turning off the automatic writing of XMP data in LRCC. The flashing then goes away.
This also happens with the NIK plug-in set so I believe it to be a problem with LR's edit in feature.
on1 suggests only using the File->Plug-ins approach as it allows more flexibility.