Corrupt DNG files?

[Frodo]

I'm exploring converting Canon CR2 raw files after processing to lossy DNGs as a way to reduce the storage my 50MP 5DsR raw files are gobbling up.  Initial experiments have shown remarkably little loss of quality even though file size is reduced by over two-thirds.  For most of my work this is fine.  For critical fine art prints, I'll pay safe and keep the raw files.
However, very occasionally I am getting what appears to be corrupt files.
I use a dual monitor set-up.  On the left is a wide gamut NEC PA242W and on the right an AOC sRGB monitor.
The first photo is in library module and both images show pink squares where I have used the LR healing brush (I removed a bright highlight in the left and the dog's tags in the middle).
The second photo is in the develop module, where the full image (NEC) still shows the pink and the editing screen (AOC) doesn't.
If I reverse the screens, the left edit screen (now the NEC) shows the pink, but the full image screen (now the AOC) doesn't.
The exported jpg is fine, but I use the NEC as my reference when editing and this obscures viewing the healing brush outcome.
Yesterday I had a job with about 200 files converted to lossy DNG.  Of these, just one showed the pink square where I had used the healing brush.  Other images where I had used the healing brush are unaffected.

These pink squares make the affected images difficult to edit.
But my bigger concern is that somehow these files might be corrupted.  This would mean that having to check all dng files before the deleting the original CR2 files, a significant extra step in my workflow.

Your thoughts would be appreciated.

Thanks, Bob

[digitaldog]

I've never seen anything like this. Have you examined the DNG's on another machine? Can you upload one to examine?

[Frodo]

Hi Andrew
Thanks for your prompt response.
This problem only occurs on the secondary monitor and persists even when I shutdown and restart the computer and LR.  My laptop (Surface 4) runs LR 6 but doesn't have a second screen.
My desktop is about a year old and runs an i7-8700 CPU with 16GB RAM.  I do not have a GPU (other than the onboard GPU).  I am running the latest update of Lightroom Classic CC
I can't get this to occur in PS because once you exit the single screen ACR, the file is converted for editing in PS.

I can't attach the file to this post as it is bigger than the maximum, but have put this in this OneDrive folder that should be accessible.
https://1drv.ms/f/s!AuxCxGijI3Y0500qsuVKdoNeYRFl

Thanks, Bob

[digitaldog]

Sounds like a display issue, not a corrupt DNG which is why I asked.

1. Check GPU settings (on or off) and try a different setting. This is found in preferences.
2. It could be a faulty ICC display profile. Recalibrate and build a new one.
3. It could be how the profile was built. Set your software to build Version 2 (V2) not V4 profiles.
4. It could be the type of profile built. Try Matrix instead of LUT based profile. Again, that's a setting in whatever software you use to calibrate and profile the display.

[digitaldog]

I can't attach the file to this post as it is bigger than the maximum, but have put this in this OneDrive folder that should be accessible.
https://1drv.ms/f/s!AuxCxGijI3Y0500qsuVKdoNeYRFl

That DNG is just fine on this end, opening in ACR, cute pup!

[Frodo]

Hi Andrew

Thanks again!
Yes, the file opens up in ACR in my computer too. But then ACR only offers a single monitor (AFAIK).

The problem seems to be with the second monitor.  My NEC is regularly caibrated using the NEC puck and Spectraview.  But the problem also occurs in the uncalibrated AOC when it is the extended monitor. I tried switching the GPU on and off in LR and that makes no difference.  I've just seen that the pink squares are also in the filmstrip.

The bit that gets me is that it is not a random corruption, glitch, whatever. It occurs where I have done an edit with the healing brush in LR before I converted the RAW file.  That was also the case in the photo from yesterday's shoot. If I reset the LR edits in the DNG file, the pink squares disappear completely, but if I undo the reset, they are back again.  But if I copy just the spot removal (healing brush) settings from the original (edited) file and paste them in the reset virtual copy, the pasting works and there are no pink squares.  So I find it hard to exclude some conversion or reading error in LR.

It does appear that the DNG file can still produce clear images, which is the main thing. 

About the pup.  A friend asked for a portrait of his partner's dog.  The dog greeted me with growling and this didn't bode well for a session on the beach. Eventually I got an indoor shot in the bag (with a terrible sunlight patch in the background), and the outside shots ended up very nice.

[Frodo]

I've now converted several hundred CR2 files into lossy DNG files without further incident.  Funny that the very first file and another in the very first batch I processed had these issues.  And now none. Long may it stay that way!