It sounds like there's a permissions problem with the folder containing the old versions of your LR presets (files ending with .lrtemplate). If LR finds any old-style .lrtemplate presets in that folder, it tries to convert them to the new .xmp format and store them in the "new" preset folder, and then it renames the .lrtemplate file so that it won't try to convert it again. But if the rename fails due to a permissions problem, LR will try to convert it again the next time you start LR.
To fix this:
1. Do Preferences > Preferences > Show All Other Lightroom Presets. That will open Mac Finder / Windows File Explorer on the "Lightroom" settings folder.
2. Move the subfolder "Develop Presets" to your Desktop.
3. Restart LR. You shouldn't see the updating-presets message.
4. Save away the "Develop Presets" folder in your Documents folder or somewhere else, just in case you might need to recover those old .lrtemplate presets.