Why do I need to to rescan to get thumbnails on some folders

[Shenstone]

I have imported about 200k images in various batches (some up to about 40K images) and I compacted and optimsed between batches which were done on different days with restarts of the PC in between 

I started noticing after a while that not all the ORF files had thumbnails (alsowat all of the JPG versions do) 

If I do a rescan with force update they all come in as per the attached screenshots 

Am I doing something wrong ?

Regards Andy

[Mario]

Did you keep the log files from the original scan process? Else we'll never know.
Do you use WIC or photools.com RAW processing? If this is a fresh IMatch 2025 installation, Edit > Preferences > Application: Prefer photools.com RAW Processing should be enabled.

When you process many files in parallel, sometimes WIC gets itself in a cinch, causing some files to have no thumbnails. But that will be logged, so if you have the log files still, we can check. The same sometimes happens with LibRaw, when too many files are processed in a session, issues "accumulate", causing some load ops to fail. This is why I recommend to process images in batches of 5K to 10K, then close and re-open IMatch to release all allocated resources, clean everything out and start fresh.

This is all based on experience. There is one billion Windows PCs out there, and users process images created over the past 30 years, with hundreds of different camera models, and processed with whatever software was used. Users store images on local spinning disks, SSDs, external disks, network storage. All this impacts things.

[Shenstone]

Sadly I did not realise that the log file was re-used and therefore i have not been able to retrieve the original one even from the recycle bin 

I doubt I will ever import so many pictures again it's just as a new user I was trying everything out

I have looked at the RAW option it was set to No which i presume was the default as I can't remember changing it - I have done so now 

My bulk storage is on HDD drives (good quality ones) and all my database and cache files are on NVME drives for speed 

I think I am unlikely to be able to replicate as I have imported 99% of my image files now so I will just do a rescan on the folders that need it 

Thanks Anyway

[Mario]

If you import 200,000 files, some issues are to be expected.The nature of the issues always varies. This is just how it is.
IMatch keeps the lof of the current session and the log of the previous session around.