It’s because multiple bounces are cached in a float_11_11_10 texture, which has one bit less precision for blue, so every next bounce will become a tiny bit more yellowish.
In practice it doesn’t happen often as albedo values shouldn’t be set so high. E.g. white paper sheet has albedo of 0.6-0.7 (in linear space). So after a few bounces even pretty white surfaces won’t add much to lighting. E.g. 0.6x0.6x0.6x0.6=0.13 so 4th bounce for a quite bright surface would add only 0.13%.