This sounds ridiculous and I don’t know if I would believe it reading this, but here is a “bug” I am experiencing. Not really something that I would notice, but in the circumstances I was in, I knew what should have been which is why I noticed so quickly.
I came to a point a few weeks ago where my Robux was 0. I have the 2200 plan for Premium, which was paid out on 12/4. Cool, 2200 exactly. Since then I have not had any Robux activity, spend, receive, nothing. A couple days ago, I noticed 40 Robux were missing, thought it was strange but amounted it to me inadvertently purchasing something or a VIP server renewal. I then noticed yesterday, the amount was 2140, 60 short this time. I checked my transactions.
At this point I have rolled out all possible possibilities that I can think of.
TL;DRL: Robux went away without trace.