There’s many things not on my side but I often can add workarounds.
For this one without a device I have no idea what I can do 
I have a Galxy A54. I tried some debugging on this with Tolriq, but we/he could not find anything, mostly because in the Symfonium logs nothing is visible, even if it happens when the logs are on (the image files are just gone). I think the issue only occurs since Android 13/OneUI 5.
I believe I can confirm that this only happens when not connected to my home network and hence to my Kodi instance. The image folder and all folders below (0 to F and the .nomedia file) seem to be newly created, they have a creation timestamp of when this last happened this morning and are empty (I have not yet connected to my home network again). When the images disappeared, there was a sync or connection attempt to the Kodi server visible in the sync/filter window, the connection,retry message was shown), which was unsuccessful obviously.
If you can repro I need logs, Symfonium NEVER delete the folder unless you click the button.
Even if the devices said that the folder does not exist when checking it should not be possible that trying to create a new one delete the previous data.
If nothing is in the logs from this morning, then there will be nothing in there. Logs where running when it happened.
Btw., the cache/images/* folders are still there and fully populated probably from the moment where I switched to persistent storage (one month ago). I would have expected them to be cleaned when I switch the image storage mode, but apart from that, it seems that they are also not cleaned by the OS. So the cleaning must somehow be triggered by the sync activity from Symfonium - not meaning, that Symfonium does delete anything, but that the OS somehow recognizes that Symfonium is now trying to access/check the images and deletes them then in that moment. They are not deleted when Symfonium is not active (like what would happen from some cleansing app that would remove the files at any arbitrary moment).
This is also something I noticed. Images seem to be wiped /redownloaded when symfonium is syncing with my plex server.
As I said I need you to check the folder content.
According to Splinter the folder was removed and everything is empty and the .nomedia have a today date.
That means the folder was deleted completely.
Next release will add logs when the clear button is called and is running to be sure that there’s not some fake clicks from Compose that would trigger it, but I can’t imagine how that would be possible.
It might make no difference, but for the record, both @lertonaut and I cache files and images on the external SD card.
You also both have Samsung that is one of the worst Android breaker 
Yeah, that was the original assumption, but I did everything that was recommended there.
You know what, i tried plex Pass yesterday and it was abysmal, i had to cancel it and got a refund. Tbh at this point using offline download with symfonium even without images is better than nothing or better than plexamp.
But if we could get images to work (even if it’s garbage Samsung) i would freakin celebrate 
At this point this is really up to both of you to be able to provide something I can work on.
Started the debug again like before.
Startd/restared Symfonium a couble of times with wifi/cellular and everything worked.
Now a couple of hours later, after starting the app again, images are gone again.
debug-20230928_181050.zip (22,8 MB)
So this log is interesting
2023-09-28 11:50:53.195 T:ImageCacheManager
Downloading image: ImageRequest(imagePath=ImagePath(file=null, url=https://aaaa?X-Plex-Token=REDACTED, shouldCache=true), cachedOnly=false, keepTransparency=false, exactSize=false, size=null, crossFade=false, debugTag=AlbumEntryGrid, sourceOnline=true)
The app download an image without error.
2023-09-28 11:50:54.448 T:ImageCacheManager
Init image cache folder at: /storage/9C33-6BBD/Android/data/app.symfonik.music.player/files/images
1 second later your device tell Symfonium that the cache folder does not exist when it tries to load from cache.
So Symfonium recreates the folders without any error (at least returned by the OS)
But then
2023-09-28 11:50:58.339 T:ImageCacheManager
Init image cache folder at: /storage/9C33-6BBD/Android/data/app.symfonik.music.player/files/images
Same thing happens 4 seconds later. This makes absolutely no sense.
Would it make sense that we try to store the image cache on the internal storage to rule out this has anything to do with the external SD card? For me that is only possible if image cache and song cache can be set separately, because the song cache would not fit on my internal storage.
We can try but this would not really be a solution.
First is to repro with 5.9.0 to be sure it’s not a compose bug. (I’ve seen Xiaomi device randomly click on compose buttons, so who knows)
Wanted to update that unfortunately still nothing resolves the issue
and images have to be reloaded every other session by scrolling down the whole offline media album list.
I tried every possible setting combination and turned off pretty much all android settings that could interfere with Symfonium.
Are there any news on your side programwise?
This happens outside of the app. If you have the persistent cache enabled. There’s nothing I can do on my side unfortunately.
There is one other thing I don’t understand. Images aren’t immediality within my offline files. Is it normal that i have to wait everytime they appear, because that is something that was a thing from the start.
Also, how come my offline songs are not affected by that disappearance but only the images, as they are in the same directory on my sd card?
I know it must be the OS’s fault but i’d like to understand why that is, if you have an idea.
No it’s not normal images are always downloaded to cache then displayed. There’s never images displayed from providers that are not cached.
The only thing I can think of is a stupid photo backup software that backup then remove them. Hence only touching images.