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.
A few hours after checking that, I notice an ADDITIONAL 100 missing, dropping it down to 2040.
At this point I have rolled out all possible possibilities that I can think of.
TL;DRL: Robux went away without trace.
Any ideas?
Honestly, I would say have a bot check your account regularly, maybe every 6 hours or something, and try to notice differences. Not sure if this is the first instance of this happening, and it may very well not be the last. What you can do is have a bot automate checking your robux balance, Guide to Web Development, and try to keep note of what you spend your robux on and see if anything mysteriously changes. I would add on to just have it console log your robux balance every 6 hours.
You likely have already done this but I feel it’s worth saying: make sure to contact Roblox Support about it. Make sure to be specific and ask for help locating any transactions that happened in the date range. You seem to have a pretty solid reason to know a transaction was deducted from your account yet no records show it. They might be able to help trace it down.
This is exactly support’s kinda job. Although this could be a site bug where it’s not showing you legitimate transactions, it could also be an account issue where funds were deducted due to Roblox backend issues, and Support should be the best equipped to investigate.
For those who are wondering or ever run into the same problem in the future, it was in fact with VIP servers. I had many active VIP servers probably for over a year that I’ve never noticed. It appears VIP server renewals do not appear in transactions, only the initial purchase.
No transactions or trades in about 2 weeks, and my 2,200 payout was less than a week ago as seen here… A few hours after checking that, I notice an ADDITIONAL 100 missing, dropping it down to 2040. 
