To suggest an answer will require some more details from you.
Please post details (screen-clip) of your Lightroom System Info. LR Menu: HELP > SYSTEM INFO...
Is your Catalog on an External Drive ?
What is the current state of the Presets Preferences option "save with the catalog" ?
What file-type are the photos you are editing in the Develop module? (proprietary raw, jpg, dng, etc)
The presets you "deleted"- were they .LRTEMPLATE or .XMP type files?
I cannot understand why there would be a reason for "presets disappearing when I switched folder".
You are talking about PRESETS and not PREVIEWS- right?
Are you storing your catalog on or off your PC internal hard drive?
Hi,thank you for such a detailled response. Here are my Lightroom information system. And my catalog is stored on my computer and not on the external hardrives (should I change that ? )
Current setting of "save presets with the cataog" is unchecked.
ALL of my presets are .XMP (created them in lightroom myself)
And here is where it clicked, I always edit RAW files but sometimes I retouch JPG images for a client and that's when the presets disappear, but not all of them, just my Users presets, the other presets folder remain untouched eventhough the only difference is that they're in separate folder.
There are complications with presets since the conversion to xmp type presets. One 'simple' explanation is that a Preset that checks the box for "Treatment & Profile" will only work for raw images , and will disappear from the preset list when editing a JPG.
"Presets including enhanced raw profiles are not visible for non-raws (Adobe Color, Monochrome, Landscape, Neutral, Portrait, Vivid)"
johnrellis is the guru on this topic!
And to quote John-
"A workaround is to modify the preset to uncheck Treatment & Profile so that the enhanced profile isn't included. But unfortunately, yet another preset bug makes that impossible when the preset includes any of the Color settings:"
The workaround in that case is to remove the Treatment & Profile from the presets using the free Fix Presets plugin.
"And my catalog is stored on my computer and not on the external hardrives (should I change that ? ) "
I do not think that is necessary. It will not change the Preset problems, and the catalog should work faster if it remains located 'internally'.