In some cases someone else creates a block a little bit before you and gets it transmitted and accepted by the network before your wallet receives that block.
Meanwhile you had created a block and received a reward that turns out to be in an orphan block and thus not accepted by the network.
The wallet then marks it red as an orphan transaction.
It happens to everyone and it does not affect your holdings nor expected staking ROI unless you are getting more orphan rewards than rewards that stick, which would indicate a reliability issue with your internet connection or computer, or most likely your system clock is not accurate. (Should be within seconds of the actual official time as reported by time.is
There was a MacOS user with this problem who seemingly had the right system time but the time told by his Mac computer to Bitcoin 2 Core app was wrong, and when he manually set his system time in MacOS settings to be correct, it fixed the problem.
Also check that you are consistently on the same block as our block explorer
and that you are connected to at least 6 peers. You can clear the orphan transactions with the "Tools" -> "Wallet Repair" -> "Recover transactions 1" tool.