Body replacement mods that make the skin naked instead effectively remove this fake underwear. To add something back, you have to equip an additional item of clothing. Many of the mods which add underwear are simply designed to provide a skimpy outfit which is worn instead of armour/clothing....
SE version source, have used it with relatively few issues so farhttps://github.com/HydrogensaysHDT/hdt-skyrimse-mods Legendary Edition (oldrim) BHUNP is your friend, this is all you will need to get body & clothing physics for most modshttps://www.nexusmods.com/skyrim/mods/100306 You ca...