Over the past month, the number of Robux in my account has been slowly increasing daily. However, there is no source of income for these Robux to be appearing. Transaction history also supports this with the number of sales and commissions being tens of thousands of Robux short of the actual account balance increase.
A private message is associated with this bug report
It might be Roblox giving you refunds from UGC items that have been deleted, though I might have misunderstood your post and actually be wrong.
This is also because refunds don’t show up in the transaction history and instead shown via messages.
Could you elaborate on exactly how much robux has been appearing in your account? Is it a large or small amount? Does it amount always increase or does it vary?
Refunds show up via messages which there have not been any of. The amount of unaccounted-for Robux is very large. Even if every UGC item I owned was deleted and refunded, it wouldn’t come close to this amount.
Specific amounts have been given to engineering privately. There is no need for it to be public. It is however a concerningly large amount of Robux that varies as though they are Robux coming from actual sales. The amount of Robux received in my account funds is multitudes higher than what transaction summary and history account for in the past month.
Could it be premium payouts possibly? Or are you receiving a % of a revenue from a group and you may not know it? Do these funds enter a pending state at all? Or are they just instantly given.
Why do you refuse to comment on the exact amounts? The exact amount of the ROBUX will help people pinpoint the issue and its source. I understand that the amount varies so it could be coming from premium payouts from a game you have made.
Could also be a mistake in a group where you have been given a group percentage (cut) of all revenue, as @yoolurs said.
This is not a public request for a review of my account by the community. Please read the original bug report for more information regarding unaccounted for Robux. The issue is these Robux are 100% accounted for including in transactions and summary. The Robux would appear in transactions and summary if they were earned those way which they were not.
This is a report for engineering which has already reached out privately and is looking into it.
Why even deny it? It’s free robux, be happy to have it! 
There was a time several years ago where some users were incorrectly given Robux and then Roblox sent a message to those users threatening to moderate their accounts if they spent that Robux before their balance was corrected.
I will always check the transaction page whenever I get earnings that I’m not familiar with, as it includes premium stipends and payouts, group payouts, and legitimate Roblox adjustments.
If Roblox is not going to tolerate the spending of invalid or glitched Robux, they should better clarify that players should contact support if they are uncertain whether they unknowingly received invalid Robux.
Thanks for the report! We’ll follow up when we have an update for you.