I just had this problem of creat #RLV folder, and it's not there. Another ALT avatar, created #RLV and it's right there as expected. Maybe this is a Friday night on SL kinda thing, or chaos theory stikes again.
The worst case this is what I had to do. I created a NOT #RLV folder, say lower case "rlv" or anything else. I then put appropriate anything in this folder, NOT named #RLV (mine was named lowercase rlv, no pound sign). Folder now has some test subfolders and a blindfodl ro something. Then after this I renamed the lower case folder "rlv", with inexpensive test subfolders or stuff in it, renamed this folder now to #rlv. Left the lowercase to best whatever was defeating the creation of #RLV.
I had checked filters, searched multiple rezzes of inventory, rebooted. Turned off RLV in collar menu, and in viewer. This was the only way I got an #rlv folder on this one avatar. SL weiredness. Be well.