I think I see the case now. Because you use an mp3 file in your original pictures, hence this is “normal” that you see this reduced bit presence at the bottom of the bit-meter (because mp3 does not have that 32 bit float full accuracy). On your 16 bit file, you don’t see that.
Coming back to your mp3 case, as soon as you process any channel, the 32 bit float range is used, then all bits are equally represented.
This means, on your 1st picture at the top of this thread, the left channel is being processed (even by just ±0.001 dB) while the right channel, is not (mp3 unprocessed signal).
I can reproduce all that now. But if my explanation was clear enough, you will understand that all this is normal and that the bit-meter is a great faithful tool