Don't use FlushGeneratedImageTask. It will "Remove all cached/generated images created as the result of an image manipulation" and "Actually clear out all the images".

All resized images inside HTMLEditors will be lost, because the path to the resized image is hardcoded in the image tag.

e.g.:
- You have "assets/Uploads/_resampled/ResizedImage200268-02.jpg" somewhere
- FlushGeneratedImageTask will remove all cached images
- "assets/Uploads/_resampled/ResizedImage200268-02.jpg" doesnt exists anymore
- edit "assets/Uploads/_resampled/ResizedImage200268-02.jpg" to "assets/Uploads/02.jpg" and save the DataObject
- a new "assets/Uploads/_resampled/ResizedImage200268-02.jpg" will be generated.

Hmmm, that's a bit of an oversight....

Okay, how about this slight change of tack. When I was calling "FlushGeneratedImagesTask", I was only concerned with flushing the resampled folder of a specific directory within "assets/".

Is there a way to flush all generated images within a certain folder only?

Sure. Write your own FlushGeneratedImagesTask?

Anyhow, cached images will be deleted if its original image get deleted. So there is really no good reason to use this task other than to have a clean state for development purposes.

@see
Image->onBeforeDelete()
Image->deleteFormattedImages()

*bump*

I seem to be having this occur on a couple of my sites (2.4.x), but not all of them. (Seemingly) random disappearance of images in various _resampled directories. The originals stick around, and the _resampled ones reappear upon saving the pages again.

However it's still not clear to me what triggers the _resampled images to be deleted, when this is occurring.

Is it happening periodically due to something like a cron job (though I can't find crontabs for any user on the system this is happening on). Or SilverStripe schedules a daily/weekly task on it's own that flushes the images? Or is it the result of some action when logged into the web-based interface to the CMS.

It's not all the images on the system. At least not one of the sites. One of the new system it did appear all of the images were disappearing after being up for a few days fine. As in maybe they were disappearing 1x a day. I'm still trying to narrow down the times this has been occurring.

Ultimately I would prefer to understand what causes the flushes, how to alleviate the behavior and why it seems to occur on some sites and not others.

@forumq42 did you have any further insight into this issue? We're experiencing this problem on our websites and it genuinely seems to have no rhyme or reason. Our sites affected are running on various versions of SilverStripe, but upward of 3.1.1.

Any insight would be much appreciated!

Hi everyone,

So you're all aware: this bug was fixed in SilverStripe 3.2. Specifically, the build task was replaced with RegenerateCachedImagesTask, which recreates the images instead of deleting them, and in so doing doesn't leave missing images.

If you're experiencing this problem, I recommend upgrading to SilverStripe 3.2 or later. If you really can't do that and what to try patching the issue yourself, you can see the relevant change here:
https://github.com/silverstripe/silverstripe-framework/pull/1723/commits/8908a6bcd7d1c6b812ecb12b2213d6f6598fd619

Thanks,
Sam